CN211579597U

CN211579597U - Photovoltaic power generation optimal arrangement system

Info

Publication number: CN211579597U
Application number: CN202020380692.8U
Authority: CN
Inventors: 刘尧; 杨昆; 郭芳; 谭喆; 陈冰; 刘仁亮; 简翔浩; 陈勇; 陆子楷; 刘超
Original assignee: China Energy Engineering Group Guangdong Electric Power Design Institute Co Ltd; Zhuhai Power Supply Bureau of Guangdong Power Grid Co Ltd
Current assignee: China Energy Engineering Group Guangdong Electric Power Design Institute Co Ltd; Zhuhai Power Supply Bureau of Guangdong Power Grid Co Ltd
Priority date: 2020-03-23
Filing date: 2020-03-23
Publication date: 2020-09-25
Anticipated expiration: 2030-03-23

Abstract

The utility model provides a photovoltaic power generation optimizes arrangement system, include: the photovoltaic module, the direct current combiner box, the photovoltaic grid-connected DC/DC device, the direct current metering cabinet and the direct current power distribution cabinet; the direct current metering cabinet and the direct current power distribution cabinet are arranged inside the direct current power distribution room, and the photovoltaic assembly, the direct current junction box and the photovoltaic grid-connected DC/DC device are arranged on the roof of the direct current power distribution room; the photovoltaic assembly is connected with the direct current combiner box, the direct current metering cabinet is connected with the direct current power distribution cabinet through a first cable, the photovoltaic grid-connected DC/DC device is connected with the direct current metering cabinet through a second cable, and the direct current combiner box is connected with the photovoltaic grid-connected DC/DC device through a third cable; the utility model discloses under the circumstances that the realization did not increase extra electrical equipment, the grid-connected PV DC/DC device provides short-circuit current's amplitude and rate of rise when can reducing interelectrode short circuit to reduce the grid-connected PV DC/DC device and provide the probability of very big short-time overcurrent.

Description

Photovoltaic power generation optimal arrangement system

Technical Field

The utility model relates to an electric power arrangement structure field especially relates to a photovoltaic power generation optimal arrangement system.

Background

With the increasingly prominent problem of fossil energy shortage, photovoltaic power generation technology is rapidly developed as a renewable power source technology. The photovoltaic power generation system is a power generation system which directly converts solar radiation energy into electric energy by utilizing the photovoltaic effect of a solar cell and is electrically connected with a public power grid. The connection to the utility grid may be in the form of alternating current or direct current. Because the photovoltaic system adopts direct current access, the photovoltaic system has higher energy efficiency, and along with the popularization and application of the direct current distribution system, the distributed photovoltaic system can be expected to adopt more direct current forms to access a direct current distribution network in the future.

At present, direct-current power grids are not completely popularized, the types of mature products of photovoltaic direct-current grid-connected DC/DC devices are not complete, most of the products need to be customized, and the price is high, so that the indoor centralized grid-connected mode is mostly adopted for distributed photovoltaic of direct-current grid-connected at present, and the cost of the grid-connected devices is saved.

Taking roofing photovoltaic as an example, in the first prior art, a photovoltaic module is usually placed on a roofing, after the photovoltaic module is converged on the roofing by a DC combiner box, a photovoltaic grid-connected DC/DC grid-connected device placed in a DC distribution room is introduced by a cable, and then the photovoltaic grid-connected DC/DC grid-connected device is subjected to DC metering and finally connected to a DC distribution cabinet, as shown in fig. 1. This prior art arrangement employs an indoor installed centralized DC/DC device, which is easy to install and implement and is widely used at the present stage. The layout shown in fig. 1 can be used for drawing a direct current grid-connected main circuit diagram of a distributed photovoltaic power generation system as shown in fig. 2.

Fig. 3 shows a topology structure of a DC/DC converter of a conventional photovoltaic power generation system, in which electric energy output by a photovoltaic array is connected via a low-voltage side (or a high-voltage side), and the high-voltage side (or the low-voltage side) is connected in parallel with a DC power grid. When a feeder-to-pole short circuit occurs, for example, f2 or f3, f4 shown in fig. 2 is short-circuited, in the arrangement shown in fig. 1, both cables L1 and L2 in fig. 2 are short (generally not more than 5m), so that the voltage across the port capacitor of the photovoltaic grid-connected DC/DC converter is reduced to an extremely low value at the moment of a short-circuit fault, and the capacitor is rapidly discharged to generate an extremely large discharge current, thereby having a serious influence on the protection, setting and the like of the whole system.

Fig. 4 shows the output current waveform of the photovoltaic power generation system when the cable L1 has a fault at the time f3 of 0.5s when the total length of the cable L2 is 10 m. It can be seen that, at the moment of a fault, the capacitor at the DC/DC port is rapidly discharged, the output current of the photovoltaic power generation system rapidly rises, reaches a peak value of 3.08kA after about 0.5ms, is 9.6 times of the rated operating current, and falls to an extremely low value after about 4.9ms, then starts to oscillate, and after about 50ms, the oscillation is finished, and the short-circuit current is completely provided by the photovoltaic array and is stabilized at 0.45 kA. The parameters used in the simulation were as follows: the rated voltage of the system is 750v, the illumination intensity is assumed to be constant and stable, the output current is 0.32kA under the normal operation of photovoltaic, the short-circuit current is 0.45kA, and the capacitance CPV at the outlet of the DC/DC converter is 3000 uF.

As can be seen from the simulation calculation results, the disadvantages of the first prior art mainly include the following aspects: 1. because the photovoltaic grid-connected DC/DC device is too close to the direct-current power distribution cabinet, the electrical distance is short, the impedance is small, when the interpolar short circuit of the feeder line occurs, the port capacitor of the grid-connected DC/DC device can be rapidly discharged to provide a great short-circuit current, and the protection misoperation and even the equipment damage are easily caused. 2. Any inter-pole feeder line short circuit can cause the grid-connected DC/DC device to discharge rapidly and provide a large short-circuit current, so that the probability of providing a large short-time overcurrent by the grid-connected DC/DC device is greatly increased on occasions with more feeder lines.

For the problem of overcurrent in the first prior art, in the second prior art, a method of connecting a current-limiting reactor in series as shown in fig. 5 is used to suppress overcurrent, that is, the current-limiting reactor is connected in series at the outlet of the photovoltaic grid-connected DC/DC converter, so as to slow down the discharging speed of the capacitor and reduce the rising rate and peak value of fault current. Fig. 6 shows the waveform of the output current of the photovoltaic power generation system when the f3 fault occurs at the time of 0.5s after the positive and negative electrodes are respectively connected in series with the 1mh current-limiting reactor, the peak value of the short-circuit current is delayed to 4.8ms, and the peak current is reduced to 1.25kA, which is about 59.4% of the peak current; after about 29ms, the fault current drops to an extremely low value, then a port capacitor of the DC/DC converter, a current limiting reactor, a line reactance and the like form an oscillation loop, and the short-circuit current continuously oscillates around 0.45 kA. As can be seen from comparison of fig. 6 with fig. 4, the peak value of the fault current, the rate of increase of the short-circuit current, and the discharge rate of the port capacitor are suppressed after the series connection of the current limiting reactors.

The series current-limiting reactance principle applied in the second prior art is simple, easy to realize and obvious in effect, and is a method generally adopted in the current engineering. However, this method also has several disadvantages: 1. the type selection of the current-limiting reactor is difficult. The iron core reactor is easy to saturate under large current and loses the current limiting function; the air-core reactor has large magnetic leakage, is easy to influence peripheral equipment, has large volume and needs larger floor area. 2. Primary equipment is added, so that project cost, occupied area and the like are correspondingly increased. Especially when rated current is great, in order to make things convenient for the reactor heat dissipation, the reactor is bulky. 3. The inductance value of the current limiting reactor is not well determined. The inductance value is too small, the current limiting effect is not obvious, the inductance value is too large, the size of the reactor is large, and system instability is easily caused. In addition, the reactor may also resonate with a capacitor or the like in the system.

Therefore, an arrangement scheme is urgently needed in the market at present, so that the amplitude and the rising rate of short-circuit current provided by the photovoltaic grid-connected DC/DC device during inter-electrode short circuit can be reduced under the condition that no additional electrical equipment is added, and the probability of extremely short-time overcurrent provided by the photovoltaic grid-connected DC/DC device is reduced.

SUMMERY OF THE UTILITY MODEL

The utility model provides a photovoltaic power generation optimizes arrangement system realizes not increasing under the condition of extra electrical equipment, and the grid-connected PV DC device provides short-circuit current's amplitude and rate of rise when can reducing interelectrode short circuit to reduce the grid-connected PV DC device and provide the probability of very big short-time overcurrent.

In order to solve the technical problem, the embodiment of the utility model provides a photovoltaic power generation optimal arrangement system is provided, include: the photovoltaic module, the direct current combiner box, the photovoltaic grid-connected DC/DC device, the direct current metering cabinet and the direct current power distribution cabinet;

the direct current metering cabinet and the direct current power distribution cabinet are arranged inside a direct current power distribution room, and the photovoltaic assembly, the direct current junction box and the photovoltaic grid-connected DC/DC device are arranged on a roof of the direct current power distribution room; the photovoltaic module is connected with the direct current combiner box, the direct current metering cabinet is connected with the direct current power distribution cabinet through a first cable, the photovoltaic grid-connected DC/DC device is connected with the direct current metering cabinet through a second cable, and the direct current combiner box is connected with the photovoltaic grid-connected DC/DC device through a third cable.

Preferably, the distance between the direct current combiner box and the photovoltaic grid-connected DC/DC device is less than 10 m; the direct current combiner box and the photovoltaic grid-connected DC/DC device are both arranged on the roof of a direct current power distribution room.

Preferably, the distance between the direct current metering cabinet and the photovoltaic grid-connected DC/DC device is greater than 100m, the direct current metering cabinet is arranged inside a direct current power distribution room, and the photovoltaic grid-connected DC/DC device is arranged on a roof of the direct current power distribution room.

Preferably, the length of the first cable is less than the length of the second cable.

Preferably, the length of the third cable is less than the length of the second cable.

Compared with the prior art, the embodiment of the utility model provides a have following beneficial effect:

1. the utility model discloses technical scheme is through setting up the photovoltaic grid-connected DC/DC device at the roofing, and all set up DC measurement cabinet and DC distribution cabinet in the inside of direct current distribution room, make the photovoltaic grid-connected DC/DC device and the connection distance of direct current measurement cabinet become long, the second cable becomes long promptly, can effectively reduce short-circuit current amplitude and rate of rise, only it is invalid to photovoltaic grid-connected DC/DC device outlet side interelectrode trouble, therefore, can reduce the photovoltaic grid-connected DC/DC device greatly and provide the probability of very big short-time overcurrent.

2. By increasing the length of the second cable, the short-circuit current amplitude and the rise rate can be effectively reduced, and the effect similar to that of a series current-limiting reactor is achieved.

3. The photovoltaic grid-connected DC/DC device is arranged in the area close to the photovoltaic module, the length of the second cable can be effectively increased, the length of the third cable can be reduced, the total length of the first cable, the second cable and the third cable is unchanged, and the cable cost and the cable loss are not additionally increased.

Drawings

FIG. 1: the photovoltaic power generation system is a schematic diagram of the arrangement structure of a photovoltaic power generation system in the prior art I;

FIG. 2: the method comprises the steps of providing a direct current grid-connected main circuit diagram of a photovoltaic power generation system in the prior art I;

FIG. 3: is a schematic diagram of a DC/DC converter topology structure of the prior art I;

FIG. 4: the method is an output current waveform diagram of a photovoltaic power generation system when the total length of cables L1 and L2 is 10m and the interpolar short circuit of feeder lines occurs in the prior art;

FIG. 5: a schematic diagram of a series current-limiting reactance method of the prior art II is shown;

FIG. 6: the output current waveform diagram of the photovoltaic power generation system is shown when the electrodes of the feeder are short-circuited after a 2mH fault current limiter is added in the prior art II;

FIG. 7: in the embodiment of the present invention, when the total length of the cables L1 and L2 is 100m, the output current waveform of the photovoltaic power generation system is in a short circuit between the feeding lines;

FIG. 8: in the embodiment of the present invention, when the total length of the cables L1 and L2 is 200m, the output current waveform of the photovoltaic power generation system is in a short circuit between the feeding lines;

FIG. 9: do the embodiment of the utility model provides an in photovoltaic power generation optimize arrangement system's schematic structure diagram.

Wherein the reference numbers of the drawings in the specification are as follows:

1. a photovoltaic module; 2. a DC combiner box; 3. a photovoltaic grid-connected DC/DC device; 4. a direct current metering cabinet; 5. A direct current power distribution cabinet; 6. a cable; 7. a direct current distribution room; 8. and (4) a roof.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts belong to the protection scope of the present invention.

Referring to fig. 1, a preferred embodiment of the present invention provides a photovoltaic power generation optimal arrangement system, including: the photovoltaic module, the direct current combiner box, the photovoltaic grid-connected DC/DC device, the direct current metering cabinet and the direct current power distribution cabinet;

The utility model discloses technical scheme is through setting up the photovoltaic grid-connected DC/DC device at the roofing, and all set up DC measurement cabinet and DC distribution cabinet in the inside of direct current distribution room, make the photovoltaic grid-connected DC/DC device and the connection distance of direct current measurement cabinet become long, the second cable becomes long promptly, can effectively reduce short-circuit current amplitude and rate of rise, only it is invalid to photovoltaic grid-connected DC/DC device outlet side interelectrode trouble, therefore, can reduce the photovoltaic grid-connected DC/DC device greatly and provide the probability of very big short-time overcurrent.

In a preferred embodiment, the distance between the DC combiner box and the pv grid-connected DC/DC device is less than 10 m; the direct current combiner box and the photovoltaic grid-connected DC/DC device are both arranged on the roof of a direct current power distribution room. In a preferred embodiment, the distance between the direct current metering cabinet and the photovoltaic grid-connected DC/DC device is greater than 100m, the direct current metering cabinet is arranged inside a direct current power distribution room, and the photovoltaic grid-connected DC/DC device is arranged on a roof of the direct current power distribution room. Specifically, the direct current combiner box and the photovoltaic grid-connected DC/DC device are arranged on the roof and are arranged adjacently. According to the scheme, the photovoltaic grid-connected DC/DC device is arranged in the area close to the photovoltaic module, the length of the second cable can be effectively increased, the length of the third cable is reduced, the total length of the first cable, the second cable and the third cable is unchanged, and the cable cost and the cable loss are not additionally increased. That is, the length of the first cable is less than the length of the second cable, and the length of the third cable is less than the length of the second cable.

The utility model discloses an increase cable L2's length, reduce cable L3's length, can effectively reduce short-circuit current amplitude and rate of rise, play the effect that is similar to series connection current-limiting reactor.

The technical principle of the present invention will be described in detail below with reference to the present technical solution.

From the analysis of the first prior art, it can be seen that the cables L1 and L2 are too short, and the system impedance is too small, which is one of the main reasons for the short-circuit current supplied by the photovoltaic power generation system to be too large (about 10 times of rated current) when the inter-electrode short circuit occurs. Fig. 7 and 8 show output current waveforms of the photovoltaic power generation system when the feeder-to-feeder short circuit occurs at 0.5s when the total length of the cables L1 and L2 is 100m and 200m, respectively. When the length of the cable reaches 100m, the short-circuit current provided by the photovoltaic system reaches 1.13kA after 3.5ms, is reduced by 63.4% compared with the length of the cable 10m, and is reduced to an extremely low value after 23ms, then begins to oscillate, and after 120ms, oscillation is finished, and the short-circuit current is completely provided by the photovoltaic array and is stabilized at 0.45 kA. When the length of the cable reaches 200m, the short-circuit current provided by the photovoltaic system reaches 0.91kA after 5.6ms, and is reduced by 70.5% compared with the short-circuit current provided by the cable with the length of 10m, and the fault current is reduced to an extremely low value after 32ms, and then begins to oscillate. Therefore, the total length of the cables L1 and L2 is increased, the amplitude and the rise rate of the short-circuit current can be effectively reduced, and the effect similar to that of a series current-limiting reactor is achieved.

Considering that the cable L1 is a connection cable between the metering cabinet and the dc distribution cabinet, in order to ensure the accuracy of metering, the metering cabinet and the dc distribution cabinet are generally not allowed to be separately arranged, and the cable L1 cannot be too long, so that the length of the cable L2 can only be increased. Because the photovoltaic module is generally arranged in an outdoor open area or a roof and the like, and a certain distance is reserved between the photovoltaic module and a direct current power distribution room, if the grid-connected DC/DC device is arranged in an area close to the photovoltaic module, the length of the cable L2 can be effectively increased, and the length of the cable L3 can be reduced, so that the cable cost and the cable loss are not additionally increased. If the grid-connected DC/DC device adopts a box body structure which can be arranged outdoors, the grid-connected DC/DC device can be arranged nearby a photovoltaic combiner box; if the grid-connected DC/DC device adopts a cabinet structure which cannot be arranged outdoors, the grid-connected DC/DC device can be arranged at an indoor position close to the photovoltaic module side. For roofing photovoltaic power generation systems, an arrangement as shown in fig. 9 may be employed. The photovoltaic module and the direct current combiner box are arranged on the roof; the photovoltaic grid-connected DC/DC device is arranged close to the direct current combiner box and is also arranged on the roof; the direct current power distribution cabinet and the direct current metering cabinet are installed in the direct current power distribution room. Electric energy generated by the photovoltaic module is collected by the direct current header box, then is connected to the photovoltaic grid-connected DC/DC device through a cable, is connected to a direct current metering cabinet in a direct current power distribution room through the cable, and finally is connected to a direct current power distribution cabinet to realize direct current grid connection.

As can be seen from fig. 2, the scheme can effectively reduce the amplitude and the rate of increase of the short-circuit current provided by the photovoltaic system for any feeder line pole faults (such as f2, f3 and f4), and is only ineffective for the outlet-side inter-pole fault (f1) of the grid-connected DC/DC device, so that the probability of providing a very short-time overcurrent for the grid-connected DC/DC device can be greatly reduced.

The utility model discloses technical scheme's advantage lies in:

1. the implementation is simple, no additional electrical equipment is added, the construction cost is low, and the occupied area is small.

2. Compare with adopting the current-limiting reactor, the utility model discloses scheme design is simple, and the effect is showing.

3. The instantaneous overcurrent amplitude and the rising rate provided by the photovoltaic power generation system during the inter-electrode short circuit of the feeder line can be effectively reduced.

4. And only when the interelectrode short circuit occurs at the outlet of the grid-connected DC/DC device, the photovoltaic power generation system can provide larger instantaneous overcurrent, so that the probability of providing the extremely short-time overcurrent by the photovoltaic power generation system is greatly reduced.

The above-mentioned embodiments further describe the objects, technical solutions and advantages of the present invention in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and are not intended to limit the scope of the present invention. It should be understood that any modification, equivalent replacement, or improvement made by those skilled in the art without departing from the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A photovoltaic power generation optimal arrangement system, characterized by comprising: the photovoltaic module, the direct current combiner box, the photovoltaic grid-connected DC/DC device, the direct current metering cabinet and the direct current power distribution cabinet;

2. The optimal photovoltaic power generation arrangement system according to claim 1, wherein the distance between the DC combiner box and the grid-connected photovoltaic DC/DC device is less than 10 m; the direct current combiner box and the photovoltaic grid-connected DC/DC device are both arranged on the roof of a direct current power distribution room.

3. The optimal photovoltaic power generation arrangement system according to claim 1 or 2, wherein the distance between the direct current metering cabinet and the photovoltaic grid-connected DC/DC device is greater than 100m, the direct current metering cabinet is arranged inside a direct current power distribution room, and the photovoltaic grid-connected DC/DC device is arranged on a roof of the direct current power distribution room.

4. The photovoltaic power generation optimized arrangement system of claim 1, wherein the first cable has a length that is less than a length of the second cable.

5. The photovoltaic power generation optimized arrangement system of claim 1, wherein the third cable has a length less than a length of the second cable.