CN220732381U - Flexible control system of box-type transformer of photovoltaic power station - Google Patents

Abstract

The utility model discloses a flexible control system of a photovoltaic power station box-type transformer in the technical field of photovoltaic power generation, and aims to solve the problem that in the prior art, no-load loss of the photovoltaic power station box-type transformer in a night standby state cannot be reduced to be close to zero, and a photovoltaic control device at a low-voltage side of a photovoltaic power generation system can work normally. The utility model can smoothly adjust the high voltage output by the box-type transformer when the photovoltaic power station is started from a standby state, so that the box-type transformer on the collecting line has no impact current in the input process, and simultaneously, the box-type transformer on the collecting line can smoothly exit at night, the control of switching of exciting inrush current is not realized at the same time when a plurality of box-type transformers on the collecting line are realized, and the photovoltaic power station can still keep the power supply of the photovoltaic control device not lost under the state of cutting at night, so that the photovoltaic power station can realize all-weather monitoring.

Description

Flexible control system of box-type transformer of photovoltaic power station

Technical Field

The utility model relates to the technical field of photovoltaic power generation, in particular to a flexible control system of a box-type transformer of a photovoltaic power station.

Background

Photovoltaic power generation is a power generation mode for converting energy by using solar energy, and does not generate power every night, all photovoltaic power generation systems are completely in a standby state for more than 12 hours, and a photovoltaic power station needs to use electricity from a power grid during the period.

The photovoltaic unit relies on solar energy to generate electricity, and at night, in the period that photovoltaic does not generate electricity, the photovoltaic inverter is in a standby state, and the main circuit is automatically powered off. However, the in-situ step-up box-type transformer connected with the photovoltaic inverter is always in an idle running state during the period of time because the in-situ step-up box-type transformer cannot be started and stopped frequently. Although the no-load loss of the transformer generally only accounts for 0.10% -0.15% of the capacity of the transformer, the photovoltaic system does not generate electricity in at least half of the day (at night), and the number of box-type transformers in the photovoltaic power station is large, the number of box-type transformers of a 100MW photovoltaic power station is generally more than 30-50, and the installation capacity is more than 100-120 MVA. Therefore, the accumulated electric energy consumption of the no-load loss of the box-type transformer of the photovoltaic power station is a larger number in one year. According to statistics, the night no-load loss of a box-type step-up transformer of a 100MW photovoltaic power station can reach 60 ten thousand degrees in a cumulative way. If the total station box-type step-up transformer can be stopped when the photovoltaic unit does not generate electricity at night, the electric energy loss of a great part can be reduced, and the operation cost is reduced by more than 30 ten thousand yuan per year.

However, due to the influence of residual magnetism of the transformer core, a large exciting inrush current is generated when the transformer is switched by a switch, impact on a power grid is equivalent to a short circuit of the transformer, and the impact current contains a large amount of direct current and harmonic components. Therefore, from the viewpoint of safe operation of the power grid, the box-type transformer of the photovoltaic power station is not allowed to start and stop intensively. If the single box-type step-up transformer is put into and out of, the influence on the power grid is small, but the operation workload of the photovoltaic power station box-type transformer is huge in the evening, and the operation workload of the photovoltaic power station box-type transformer is huge in the morning, so that the operation of most photovoltaic power stations is unrealistic. In addition, when the transformer is put into operation, the exciting surge current has larger electric power impact on the transformer, frequent operation is carried out once a day, the electric power impact caused by the impact current also can greatly influence the insulation of the transformer, and the service life of the transformer is reduced.

For the above reasons, the box-type step-up transformer is in an idle running state when the photovoltaic power station does not generate electricity at night. If the box-type transformer of the photovoltaic power station can be automatically and flexibly controlled to start and stop under the premise of not generating impact on the power grid and the box-type transformer, the box-type step-up transformer of the photovoltaic power station can smoothly exit from operation without impact when entering the night without generating time, and the box-type step-up transformer of the photovoltaic power station can be smoothly put into operation without impact when entering the generating time during the daytime without impact, so that the no-load loss of the transformer of the photovoltaic power station at night can be greatly saved, the operation cost of the photovoltaic power station is reduced, and the operation efficiency and the economic benefit of the photovoltaic power station are improved.

At present, the prior art can completely reduce the voltage of a photovoltaic power station night photovoltaic power generation system to 0V, so that the no-load loss of a box-type transformer is reduced to approach zero, but the power supply of a photovoltaic control device at the low-voltage side of the photovoltaic power generation system is reduced to 0V, so that the photovoltaic power station cannot work normally, and the monitoring of the night working condition of the photovoltaic power generation system by the photovoltaic dispatching system is influenced.

Disclosure of Invention

The utility model aims to overcome the defects in the prior art, provides a flexible control system of a photovoltaic power station box-type transformer, and solves the problem that the current no-load loss of the photovoltaic power station box-type transformer cannot be reduced to be close to zero, and a photovoltaic control device at the low-voltage side of a photovoltaic power generation system can work normally.

In order to solve the technical problems, the utility model is realized by adopting the following technical scheme:

the utility model provides a flexible control system of a box-type transformer of a photovoltaic power station, which comprises the following components: the load switch is connected in series between the collector wire voltage input end and the collector wire voltage output end;

the high-voltage side of the step-down transformer is connected with the voltage input end of the collecting line, the low-voltage side of the step-down transformer is divided into two paths, one path is respectively connected with the standby power interfaces of all the two-path power switching devices, the other path is sequentially connected with the low-voltage converter in series, and the first alternating current contactor is connected to the low-voltage side of any box-type transformer in the photovoltaic power station;

the number of the two-way power supply switching devices corresponds to the number of the box-type transformers in the photovoltaic power station, the main power supply interfaces of one two-way power supply switching device are connected with the low-voltage sides of the corresponding box-type transformers, and the supply end is connected with the power supply end of the photovoltaic control device for monitoring the box-type transformers.

Further, a high-voltage fuse and an isolating switch are sequentially connected in series between the high-voltage side of the step-down transformer and the voltage input end of the collecting wire.

Further, the method further comprises the following steps: a first charge indicator, a second charge indicator, a third charge indicator, and a fourth charge indicator;

the input end of the first charge indicator is connected between the voltage input end of the collector wire and the load switch, and the input end of the second charge indicator is connected between the load switch and the voltage output end of the collector wire;

the input end of the third charge indicator is connected between the voltage input end of the collecting wire and the isolating switch, and the input end of the fourth charge indicator is connected between the high-voltage side of the step-down transformer and the high-voltage fuse.

Further, the method further comprises the following steps: the first lightning arrester, the second lightning arrester and the third lightning arrester;

the input end of the first lightning arrester is connected between the voltage input end of the electric collecting wire and the load switch, the input end of the second lightning arrester is connected between the voltage input end of the electric collecting wire and the isolating switch, and the input end of the third lightning arrester is connected with the low-voltage side of the step-down transformer.

Furthermore, the low-voltage side of the step-down transformer is divided into two paths after being connected with an outlet switch in series, one path is connected with a first low-voltage switch in series and then is connected with the standby power interfaces of all the two-path power switching devices respectively, and the other path is connected with a second low-voltage switch in series and then is connected with a low-voltage converter and a first alternating-current contactor in series in sequence and then is connected to the low-voltage side of any box-type transformer in the photovoltaic power station.

Further, the low-voltage converter includes: the soft start device comprises a soft start switch, a reactor, a three-phase full-bridge rectifying circuit, a supporting capacitor, an IGBT three-phase full-bridge inverter circuit, a filter and a step-up transformer;

the soft start switch is connected with the reactor in series, the output end of the reactor is connected with the alternating current input end of the three-phase full-bridge rectifying circuit, the direct current output end of the three-phase full-bridge rectifying circuit is connected with the supporting capacitor in parallel, the supporting capacitor is connected with the direct current input end of the IGBT three-phase full-bridge inverting circuit in parallel, and the alternating current output end of the IGBT three-phase full-bridge inverting circuit is sequentially connected with the filter and the step-up transformer in series.

Further, the two-way power supply switching device includes: the device comprises a main power supply interface, a standby power supply interface, a supply end, a second alternating current contactor, a third alternating current contactor and a control relay;

the main power supply interface is connected with the supply end through a second alternating current contactor, the standby power supply interface is connected with the supply end through a third alternating current contactor, and the power supply end of the control relay is connected with the main power supply interface;

the normally open contact of the control relay is connected with the power supply end of the second alternating current contactor, and the normally closed contact of the control relay is connected with the power supply end of the third alternating current contactor.

Compared with the prior art, the utility model has the following beneficial effects:

1. according to the utility model, through the load switch, the step-down transformer and the low-voltage converter which are connected in series to the collecting line of the photovoltaic power station, when the photovoltaic power station is started from a standby state, the high voltage output by the box-type transformer can be smoothly regulated, so that no impact current exists in the input process of the box-type transformer on the collecting line, the smooth exit of the box-type transformer in the night standby state of the photovoltaic power station is realized, and the loss of the photovoltaic power station is greatly reduced;

2. according to the utility model, the flexible control of the box-type transformers of the photovoltaic power station is realized through the step-down transformer and the low-voltage converter, the night no-load loss of the box-type transformers is eliminated, no impact current is generated in the control process, and meanwhile, the simultaneous excitation-free inrush current switching control of a plurality of box-type transformers on a power collecting line is realized;

3. according to the utility model, through the step-down transformer and the two-way power supply switching device, the power supply of the photovoltaic power station can still be kept from losing in the night cut-off state, so that the photovoltaic power station can realize all-weather monitoring.

Drawings

The accompanying drawings are included to provide a further understanding of the utility model and are incorporated in and constitute a part of this specification, illustrate the utility model and together with the embodiments of the utility model, serve to explain the utility model. In the drawings:

fig. 1 is an electrical schematic diagram of a flexible control system for a photovoltaic power plant box transformer provided by an embodiment of the present utility model;

fig. 2 is a wiring diagram of a flexible control system of a photovoltaic power station box-type transformer provided by an embodiment of the present utility model;

FIG. 3 is a control circuit diagram of a low voltage converter in the flexible control system of the photovoltaic power plant box transformer shown in FIG. 2;

FIG. 4 is a control circuit diagram of a two-way power switching device in the flexible control system of the photovoltaic power plant box transformer shown in FIG. 1;

in the figure: 1. a load switch; 2. a step-down transformer; 3. a low voltage current transformer; 31. a soft start switch; 32. a reactor; 33. a three-phase full-bridge rectifier circuit; 34. a supporting capacitor; 35. IGBT three-phase full bridge inverter circuit; 36. a filter; 37. a step-up transformer; 4. a first ac contactor; 5. a two-way power supply switching device; 51. a main power interface; 52. a standby power interface; 53. a supply end; 54. a second ac contactor; 55. a third ac contactor; 56. a control relay; 6. a high voltage fuse; 7. an isolating switch; 8. a first charge indicator; 9. a second charge indicator; 10. a third charge indicator; 11. a fourth charge indicator; 12. a first lightning arrester; 13. a second lightning arrester; 14. a third lightning arrester; 15. an outlet switch; 16. a first low voltage switch; 17. and a second low voltage switch.

Detailed Description

The utility model is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present utility model, and are not intended to limit the scope of the present utility model.

Examples

As shown in fig. 1, the embodiment of the utility model provides a flexible control system for a box-type transformer of a photovoltaic power station, which comprises a load switch 1, a step-down transformer 2, a low-voltage converter 3, a first alternating-current contactor 4 and a double-circuit power supply switching device 5, wherein the load switch 1 is connected in series between a collector line voltage input end and a collector line voltage output end, the box-type transformer, a low-voltage circuit breaker, a photovoltaic light-emitting array and a box-type transformer photovoltaic control device power supply can be a plurality of groups, and the collector line voltage output end is sequentially connected in series with the box-type transformer, the low-voltage circuit breaker, the photovoltaic light-emitting array and the box-type transformer photovoltaic control device power supply corresponding to each group.

In this embodiment, the normal working voltage of the collecting line is 35KV, and the output voltage of the photovoltaic power generation array is 0.8KV, so that the box-type transformer is a step-up transformer of 0.8KV/35KV, and the working voltage of the photovoltaic control device is 800V, so that each device in the photovoltaic power station can work normally.

The high-voltage side of the step-down transformer 2 is connected with the voltage input end of the collecting line, the low-voltage side of the step-down transformer 2 is divided into two paths, one path is respectively connected with the standby power interfaces 52 of the two-path power switching devices 5, the other path is sequentially connected with the low-voltage converter 3 in series, and the first alternating current contactor 4 is connected to the low-voltage side of any box-type transformer in the photovoltaic power station.

It can be understood that the step-down transformer 2 in the present embodiment is: the 35kV/0.8kV step-down transformer, so that the voltage of the low-voltage side is 800V, and the normal working requirement of the photovoltaic control device can be met.

The number of the two-way power supply switching devices 5 corresponds to the number of the box-type transformers in the photovoltaic power station, the main power supply interface 51 of one two-way power supply switching device 5 is connected with the low-voltage side of the corresponding box-type transformer, and the supply end 53 is connected with the power supply end of the photovoltaic control device for monitoring the box-type transformer.

It should be noted that, the photovoltaic control device is used for monitoring the night working condition of the photovoltaic power generation system, so each group of photovoltaic power generation arrays is configured with one photovoltaic power generation array to realize the full-coverage type monitoring requirement.

The working principle is that;

in the non-power generation standby state of the photovoltaic power station at night, the whole current collecting circuit is cut off through the breaking load switch 1, so that box-type transformers of a plurality of photovoltaic power generation units connected in parallel under the circuit are powered off. Before the photovoltaic power station generates electricity in daytime, a voltage of 0-800V is smoothly emitted through a low-voltage converter 3 at the low-voltage side of a 35kV/0.8kV step-down transformer 2, the voltage is connected to the low-voltage side of any box-type step-down transformer, and the voltage at the high-voltage side of each box-type transformer on the current collecting circuit is smoothly boosted to 35kV through the boosting function of the box-type transformer, and the voltage amplitude and the phase are completely consistent with those of the 35kV power grid side. At this time, the load switch 1 is closed, and the 35kV current collecting line can be newly put into the state without impact.

Since the voltage amplitude and the phase of the two ends of the load switch 1 are completely consistent before the load switch is put into operation, the inrush current is not impacted in the input process. The low-voltage side of the 35kV/0.8kV step-down transformer 2 can also provide a working power supply of a photovoltaic control device under a photovoltaic power generation unit at night, and under the working condition of electrified operation of a box-type transformer in daytime, the working power supply can be automatically switched by the 800V double-circuit power supply switching device 5: the operating power of the photovoltaic control device is switched back to being supplied by the low voltage side of the box transformer.

Embodiment two:

as shown in fig. 2, the present embodiment provides a flexible control system for a box-type transformer of a photovoltaic power station, which is different from the first embodiment in that a high-voltage fuse 6 and an isolating switch 7 are sequentially connected in series between the high-voltage side of the step-down transformer 2 and the voltage input end of the collector line.

Specifically, when the step-down transformer 2 is electrified and normally works, the high-voltage fuse 6 and the isolating switch 7 are in a closed state, the working current of the high-voltage fuse 6 is the same as that of the step-down transformer 2, if the step-down transformer 2 has a short circuit fault, the fuse wire of the high-voltage fuse 6 is blown, so that the overcurrent protection of the transformer is realized, and then the isolating switch 7 can be manually disconnected to power off the step-down transformer 2 and exit from the running state.

As shown in fig. 2, in this embodiment, further includes: a first charge indicator 8, a second charge indicator 9, a third charge indicator 10, and a fourth charge indicator 11; the input end of the first charge indicator 8 is connected between the collector wire voltage input end and the load switch 1, and the input end of the second charge indicator 9 is connected between the load switch 1 and the collector wire voltage output end; the input end of the third charge indicator 10 is connected between the voltage input end of the collecting wire and the isolating switch 7, and the input end of the fourth charge indicator 11 is connected between the high-voltage side of the step-down transformer 2 and the high-voltage fuse 6.

Specifically, the first charge indicator 8 and the second charge indicator 9 may display the charge state of the load switch 1 before and after the disconnection or the closing of the switch, and the third charge indicator 10 and the fourth charge indicator 11 may display the charge state of the high voltage fuse 6 before and after the fuse is blown, so that the whole control system may be fully monitored.

As shown in fig. 2, in this embodiment, further includes: a first arrester 12, a second arrester 13 and a third arrester 14; the input end of the first lightning arrester 12 is connected between the voltage input end of the collector wire and the load switch 1, the input end of the second lightning arrester 13 is connected between the voltage input end of the collector wire and the isolating switch 7, and the input end of the third lightning arrester 14 is connected with the low-voltage side of the step-down transformer 2.

Specifically, the first arrester 12 and the second arrester 13 can suppress the operation overvoltage on the collector line side, and the third arrester 14 can suppress the overvoltage on the low voltage side of the step-down transformer 2, whereby the control system can be sufficiently protected.

As shown in fig. 2, in this embodiment, the low-voltage side of the step-down transformer 2 is divided into two paths after being connected in series with a line outlet switch 15, one path is connected in series with a first low-voltage switch 16 and then is respectively connected with the standby power interfaces 52 of the two-path power switching devices 5, and the other path is connected in series with a second low-voltage switch 17 and then is sequentially connected in series with the low-voltage converter 3 and the first ac contactor 4 to be connected to the low-voltage side of any box-type transformer in the photovoltaic power station.

Specifically, the first low-voltage switch 16 and the second low-voltage switch 17 can be disconnected to power off the 2-path 800V outgoing line, so that the maintenance of operators can be facilitated. In addition, 2 paths of 800V outgoing lines can be powered off simultaneously by disconnecting the outgoing line switch 15, so that the operation is convenient, and the overhaul efficiency is improved.

As shown in fig. 3, in the present embodiment, the low-voltage converter 3 includes: soft start switch 31, reactor 32, three-phase full-bridge rectifier circuit 33, support capacitor 34, IGBT three-phase full-bridge inverter circuit 35, filter 36 and step-up transformer 37; the soft start switch 31 is connected in series with the reactor 32, the output end of the reactor 32 is connected with the alternating current input end of the three-phase full-bridge rectifying circuit 33, the direct current output end of the three-phase full-bridge rectifying circuit 33 is connected in parallel with the supporting capacitor 34, the supporting capacitor 34 is connected in parallel with the direct current input end of the IGBT three-phase full-bridge inverter circuit 35, and the alternating current output end of the IGBT three-phase full-bridge inverter circuit 35 is sequentially connected in series with the filter 36 and the step-up transformer 37.

Specifically, the low-voltage converter 3 inputs an 800V three-phase ac voltage, firstly, the three-phase ac voltage passes through a resistor and a reactor 32 of the soft start switch 31, the input transient impact current can be restrained, then, the three-phase full-bridge rectifying circuit 33 is input, the rectifying function of rectifying the ac 800V voltage to a dc 1100V is realized, a supporting capacitor 34 on a dc bus is used for stabilizing the dc 1100V voltage, the dc voltage realizes the inverting function of outputting the ac voltage of 0-400V through a next IGBT three-phase full-bridge inverter circuit 35, a filter 36 is formed by the reactor and the capacitor on an output line, the higher harmonic wave of the ac voltage output by the inverter can be filtered, and the ac voltage output of 0-800V can be formed after the voltage is boosted by the booster transformer 37.

As shown in fig. 3, in the present embodiment, the two-way power switching device 5 includes: a main power interface 51, a standby power interface 52, a supply terminal 53, a second ac contactor 54, a third ac contactor 55, and a control relay 56; the main power interface 51 is connected with the supply end 53 through the second alternating current contactor 54, the standby power interface 52 is connected with the supply end 53 through the third alternating current contactor 55, and the power supply end of the control relay 56 is connected with the main power interface 51; the normally open contact of the control relay 56 is connected to the power supply end of the second ac contactor 54, and the normally closed contact of the control relay 56 is connected to the power supply end of the third ac contactor 55.

The working principle is as follows:

when the main power supply and the standby power supply are powered, the control relay 56 works, the normally open contact of the control relay 56 is closed, the normally closed contact is opened, then the second alternating current contactor 54 is powered, the coil of the second alternating current contactor is electrified to attract the switch, the third alternating current contactor 55 is not powered, the coil of the third alternating current contactor is not electrified to break the switch, so that the main power supply supplies power to the photovoltaic control device through the closed second alternating current contactor 54, and the standby power supply cannot supply power to the photovoltaic control device due to the breaking of the third alternating current contactor 55.

When the main power supply is powered off and the standby power supply is powered on, the control relay 56 does not work, the normally open contact of the control relay 56 is opened, the normally closed contact is closed, then the second alternating current contactor 54 is not electrified, the coil of the second alternating current contactor is not electrified to break the switch, the third alternating current contactor 55 is electrified, the coil of the third alternating current contactor is electrified to attract the switch, the main power supply can not supply power to the photovoltaic control device due to the breaking of the second alternating current contactor 54, and the standby power supply supplies power to the photovoltaic control device through the closed third alternating current contactor 55.

According to the utility model, the load switch 1, the step-down transformer 2 and the low-voltage converter 3 connected in series to the collecting circuit of the photovoltaic power station can smoothly adjust the high voltage output by the box-type transformer when the photovoltaic power station is started from the standby state, so that the box-type transformer on the collecting circuit has no impact current in the input process, the smooth withdrawal of the box-type transformer in the night standby state of the photovoltaic power station is realized, the loss of the photovoltaic power station is greatly reduced, and the aim that the power supply of the photovoltaic control device is not lost is fulfilled.

The foregoing is merely a preferred embodiment of the present utility model, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present utility model, and such modifications and variations should also be regarded as being within the scope of the utility model.

Claims (7)

1. A flexible control system for a photovoltaic power plant box transformer, comprising: the load switch (1) is connected in series between the collector line voltage input end and the collector line voltage output end;

the high-voltage side of the step-down transformer (2) is connected with the voltage input end of the collector wire, the low-voltage side of the step-down transformer (2) is divided into two paths, one path is respectively connected with the standby power interfaces (52) of the two-path power switching devices (5), the other path is sequentially connected with the low-voltage converter (3) in series, and the first alternating-current contactor (4) is connected to the low-voltage side of any box-type transformer in the photovoltaic power station;

the number of the two-way power supply switching devices (5) corresponds to the number of the box-type transformers in the photovoltaic power station, a main power supply interface (51) of one two-way power supply switching device (5) is connected with the low-voltage side of the corresponding box-type transformer, and a supply end (53) is connected with a power supply end of a photovoltaic control device for monitoring the box-type transformer.

2. The flexible control system of a photovoltaic power station box-type transformer according to claim 1, characterized in that a high voltage fuse (6) and a disconnecting switch (7) are connected in series in sequence between the high voltage side of the step-down transformer (2) and the collector line voltage input.

3. The flexible control system of a photovoltaic power plant box transformer of claim 2, further comprising: a first charge indicator (8), a second charge indicator (9), a third charge indicator (10) and a fourth charge indicator (11);

the input end of the first charge indicator (8) is connected between the collector wire voltage input end and the load switch (1), and the input end of the second charge indicator (9) is connected between the load switch (1) and the collector wire voltage output end;

the input end of the third charge indicator (10) is connected between the voltage input end of the collecting wire and the isolating switch (7), and the input end of the fourth charge indicator (11) is connected between the high-voltage side of the step-down transformer (2) and the high-voltage fuse (6).

4. The flexible control system of a photovoltaic power plant box transformer of claim 2, further comprising: a first arrester (12), a second arrester (13) and a third arrester (14);

the input end of the first lightning arrester (12) is connected between the voltage input end of the electric collecting wire and the load switch (1), the input end of the second lightning arrester (13) is connected between the voltage input end of the electric collecting wire and the isolating switch (7), and the input end of the third lightning arrester (14) is connected with the low-voltage side of the step-down transformer (2).

5. The flexible control system of a photovoltaic power station box-type transformer according to claim 2, wherein the low-voltage side of the step-down transformer (2) is divided into two paths after being connected with an outlet switch (15) in series, one path is connected with a first low-voltage switch (16) in series and then is respectively connected with a standby power interface (52) of each two-path power switching device (5), the other path is connected with a second low-voltage switch (17) in series and then is sequentially connected with the low-voltage converter (3) in series, and the first alternating-current contactor (4) is connected to the low-voltage side of any box-type transformer in the photovoltaic power station.

6. The flexible control system of a photovoltaic power plant box transformer according to claim 1, characterized in that said low-voltage converter (3) comprises: the soft start device comprises a soft start switch (31), a reactor (32), a three-phase full-bridge rectifying circuit (33), a supporting capacitor (34), an IGBT three-phase full-bridge inverter circuit (35), a filter (36) and a step-up transformer (37);

the soft start switch (31) is connected with the reactor (32) in series, the output end of the reactor (32) is connected with the alternating current input end of the three-phase full-bridge rectifying circuit (33), the direct current output end of the three-phase full-bridge rectifying circuit (33) is connected with the supporting capacitor (34) in parallel, the supporting capacitor (34) is connected with the direct current input end of the IGBT three-phase full-bridge inverter circuit (35) in parallel, and the alternating current output end of the IGBT three-phase full-bridge inverter circuit (35) is sequentially connected with the filter (36) and the step-up transformer (37) in series.

7. The flexible control system of a photovoltaic power plant box transformer according to claim 1, characterized in that said two-way power switching device (5) comprises: a main power interface (51), a standby power interface (52), a supply terminal (53), a second ac contactor (54), a third ac contactor (55) and a control relay (56);

the main power interface (51) is connected with the supply end (53) through a second alternating current contactor (54), the standby power interface (52) is connected with the supply end (53) through a third alternating current contactor (55), and the power supply end of the control relay (56) is connected with the main power interface (51);

the normally open contact of the control relay (56) is connected with the power supply end of the second alternating current contactor (54), and the normally closed contact of the control relay (56) is connected with the power supply end of the third alternating current contactor (55).