CN114552565A - Direct current bus system and control method thereof - Google Patents

Abstract

The invention provides a direct current bus system and a control method thereof, wherein the direct current bus system comprises: the system comprises at least one power grid, at least one double-splitting transformer, a first subsystem and a second subsystem, wherein the first subsystem and the second subsystem are connected to the output end of the double-splitting transformer in parallel, and are distributed in the same layout and in a symmetrical mode; a common negative direct current bus of the first subsystem; the real-time power of the first subsystem and the real-time power of the second subsystem are equal, and the sum of current vectors of the first subsystem and the second subsystem on the direct-current negative bus is controlled to be zero. The invention can solve the problem of asymmetric voltage on the bus and reduce the line loss.

Description

Direct current bus system and control method thereof

Technical Field

The invention belongs to the technical field of power transformation and distribution, and particularly relates to a direct-current bus system and a control method thereof.

Background

Fig. 1 shows an embodiment 100 of a DC bus system in the prior art, a power grid 110 is connected to an AC/DC converter 130 via a first switch 120 to establish a DC bus voltage, and a distributed photovoltaic system 140, an energy storage battery 150, an electric vehicle 160 and other DC loads 170 are directly connected to a DC bus 180, which is simple in structure. However, for a large-capacity dc system, the line voltage boosting is affected by the withstand voltage of each power conversion device, and conventionally, only a 750V dc system can be achieved, at this time, the line loss is large, if the line loss is further reduced, the line voltage needs to be boosted, for example, to 1500V, for a high-power rectifier or an electric device, a high-voltage IGBT device or a three-level technology based on a 1200V device may be adopted, but the method is not applicable to MOS device technology routes in which many medium and small-power electric devices and charging devices are based on 600V.

Fig. 2 shows another embodiment 200 of the DC bus system, which is different from the DC bus architecture shown in fig. 1 in that a DC negative bus 290 is added, a power grid 210 is connected to an AC/DC converter 230 through a first switch 220 to establish a DC bus voltage, and a distributed photovoltaic system 240, an energy storage battery 250, an electric vehicle 260 and other DC loads 270 are connected between a DC bus 280 and the DC negative bus 290, so that there is a problem of zero potential drift, and a problem of non-uniform voltage of the positive and negative half bus voltages is prominent, and in order to solve the offset problem, complexity of device control is increased.

Disclosure of Invention

Aiming at the problems, the invention provides a direct current bus system which can solve the problem of asymmetric voltage on a bus and reduce the line loss.

In order to achieve the purpose, the invention mainly adopts the following technical scheme:

at least one electrical grid;

the double-split transformer is connected with a power grid;

the first subsystem and the second subsystem are connected to the output end of the double-split transformer in parallel, and are distributed in the same layout and in a symmetrical mode;

the first subsystem comprises a first direct current positive bus, the second subsystem comprises a second direct current positive bus, real-time voltages on the first direct current positive bus and the second direct current positive bus are equal in size and opposite in direction, the first subsystem and the second subsystem share a direct current negative bus, and the sum of current vectors of the first subsystem and the second subsystem on the direct current negative bus is zero.

In some embodiments, the first subsystem includes a first AC/DC converter, the second subsystem includes a second AC/DC converter, an input terminal of the first AC/DC converter is connected to one output terminal of the double-split transformer through a first switch, an input terminal of the second AC/DC converter is connected to another output terminal of the double-split transformer through a first switch, an output terminal of the first AC/DC converter is connected to the first direct current positive bus, and an output terminal of the second AC/DC converter is connected to the second direct current positive bus.

In some embodiments, the first direct current positive bus and the second direct current positive bus are respectively connected with an alternating current load through a DC/AC converter.

In some embodiments, the first direct current positive bus and the second direct current positive bus are respectively connected with a direct current load through a DC/DC converter.

In some embodiments, the first subsystem further includes a first ac bus, the second subsystem further includes a second ac bus, the first ac bus and the second ac bus are respectively connected to the double-split transformer through a first switch, and at least 1 ac load is connected to the first ac bus and the second ac bus.

In some embodiments, the first positive DC bus is connected to an AC load on the first AC bus via a DC/AC converter, and the second positive DC bus is connected to an AC load on the second AC bus via a DC/AC converter.

In some embodiments, a second switch is disposed between the first ac bus and the first switch, and a third switch is disposed between the second ac bus and the first switch.

In some embodiments, the power grid system comprises a first double-splitting transformer, a second double-splitting transformer, a first power grid and a second power grid, wherein the first double-splitting transformer is connected with the first power grid, the second double-splitting transformer is connected with the second power grid, one end of each of the first subsystem and the second subsystem is connected to the output end of the first double-splitting transformer, and the other end of each of the first subsystem and the second subsystem is connected to the output end of the second double-splitting transformer.

Aiming at the direct current bus system, the invention also provides a control method of the direct current bus system, which comprises the following steps:

step S1: acquiring real-time load data on a direct current positive bus, and judging the working mode of the direct current positive bus;

step S2: if the direct current positive bus works in a heavy load mode, energy storage adjustment is carried out, so that the sum of the current vectors of the common direct current negative bus is zero, and power balance on the direct current positive bus is realized;

step S3: and if the direct current positive bus works in a light load mode, the first AC/DC converter or the second AC/DC converter is regulated to work intermittently.

In some embodiments, the step S3 further includes:

step 31: in the starting stage of the first AC/DC converter or the second AC/DC converter, the direct current positive bus and the photovoltaic system supply power to the load together;

step 32: during the shutdown phase of the first AC/DC converter or the second AC/DC converter, the difference of the load energy is provided by the photovoltaic system and the energy storage device.

According to the direct current bus system provided by the invention, after the voltage class conversion of the power grid voltage is carried out by the double-split transformer, the power grid voltage respectively supplies power to the first subsystem and the second subsystem, each subsystem operates independently, the first bus and the second bus operate based on respective independent voltage sources, the first bus and the second bus do not influence each other, and the power supply safety is improved. The photovoltaic system, the energy storage battery, the electric automobile and other direct current loads are respectively designed on the first direct current positive bus and the second direct current positive bus, so that systematic unified scheduling control can be realized, independent optimization control can be realized for the first direct current positive bus and the second direct current positive bus, and the flexibility of the system is improved. The direct current bus system provided by the invention combines the real-time data acquisition of distributed power generation and load of the first direct current positive bus and the second direct current positive bus, and adjusts the charging and discharging states and real-time numerical values of the distributed energy storage devices of the first direct current positive bus and the second direct current positive bus, so that the power of the first direct current positive bus and the power of the second direct current positive bus can be adjusted, and the line loss is reduced.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings according to the drawings.

Fig. 1 is a schematic structural diagram of an embodiment of a prior art dc bus system.

Fig. 2 is a schematic structural diagram of another embodiment of a dc bus system in the prior art.

Fig. 3 is a schematic structural diagram of a first embodiment of a dc bus system provided in the present invention.

Fig. 4 is a schematic structural diagram of a second embodiment of the dc bus system provided in the present invention.

Fig. 5 is a schematic structural diagram of a third embodiment of the dc bus system provided in the present invention.

Fig. 6 is a schematic structural diagram of a fourth embodiment of the dc bus system provided in the present invention.

Fig. 7 is a flowchart of a method for controlling a dc bus system according to the present invention.

Description of reference numerals:

100. 200, 300, 400, 500, 600-direct current bus system;

130. 230-AC/DC converter, 140, 240-photovoltaic system, 150, 250-energy storage battery, 160, 260-electric vehicle, 170, 270-direct current load, 180, 280-direct current positive bus, 290-direct current negative bus;

310. 410, 510-a first subsystem, 320, 420, 520-a second subsystem, 110, 210, 330, 430-a grid, 531-a first grid, 532-a second grid, 340, 440-a double split transformer, 541-a first split transformer, 542-a second split transformer, 120, 220, 350, 450, 551-a first switch, 311, 411, 511-a first direct current positive bus, 321, 421, 524-a second direct current positive bus, 312, 412-a first AC/DC converter, 322, 422-a second AC/DC converter, 413, 513-a first alternating current bus, 423, 523-a second alternating current bus, 414, 514-a second switch, 424, 524-a third switch, 552-a fourth switch.

Detailed Description

The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.

As shown in fig. 3, the present invention provides a dc bus system 300, which includes a power grid 330, a dual-split transformer 340, a first subsystem 310 and a second subsystem 320, wherein the dual-split transformer 340 is connected to the power grid 330, the first subsystem 310 and the second subsystem 320 are connected to the power grid 330 through the dual-split transformer 340, and obtain power from the power grid 330 side, and perform voltage class conversion through the dual-split transformer 340. The first subsystem 310 and the second subsystem 320 are respectively connected in parallel to the output end of the double split transformer 340 through a first switch 350.

As shown in fig. 3, the first subsystem 310 and the second subsystem 320 are arranged in the same and symmetrical manner, the first subsystem 310 includes a first AC/DC converter 312, the second subsystem 320 includes a second AC/DC converter 322, and the input terminals of the first AC/DC converter 312 and the second AC/DC converter 322 are respectively connected to a double split transformer 340 through a first switch 350. The output end of the first AC/DC converter 312 is connected with the first direct current positive bus 311 and the direct current negative bus 312, the output end of the second AC/DC converter 312 is connected with the positive bus 321 and the direct current negative bus 312, the voltage range of the first direct current positive bus 311 is between-Vbus-0V, the voltage range of the second direct current positive bus 321 is between 0V and + Vbus, and all the devices including the DC/AC converter and the AC/DC converter bear half of the grid voltage and are equivalent to a double-voltage bus of a conventional direct current bus system.

The first subsystem 310 and the second subsystem 320 are respectively connected with a photovoltaic system, an energy storage battery, an electric vehicle and other direct current loads through different DC/DC converters, or are connected with various alternating current loads through DC/AC converters. The first subsystem 310 and the second subsystem 320 are in a symmetrical distribution structure with the same layout.

When the power grid 330 is powered off, the system can be rapidly started to operate in an off-grid state, and the energy storage battery, the electric automobile and the photovoltaic system are controlled to supply power for the electric equipment in order.

According to practical environment and practical application requirements, in some embodiments, the dc bus system 300 may further include a plurality of subsystems with the same layout and symmetrical distribution, which are paired with the first subsystem 310 and the second subsystem 320, to supply power to different energy storage batteries, electric vehicles, dc loads, and ac loads.

As shown in fig. 4, the structure of the dc bus system 400 is similar to that of the dc bus system 300, and includes a first subsystem 410 and a second subsystem 420 which are arranged in the same layout and are distributed symmetrically, and the first subsystem 410 and the second subsystem 420 are respectively connected to a double-split transformer 440 through a first switch 450, so as to obtain power from a side of a power grid 430. In the first subsystem 410, the first ac bus 413 is connected to the output terminal of the first switch 450 through the second switch 414; in the second subsystem 420, a second ac busbar 423 is connected to the output of the first switch 450 via a third switch 424. Alternating current loads with the same number are symmetrically connected to the first alternating current bus 413 and the second alternating current bus 423, in some embodiments, the first direct current positive bus 411 and the second direct current positive bus 421 can respectively supply power to the alternating current loads on the first alternating current bus 413 and the second alternating current bus 423 through a DC/AC converter, and when the power grid 430 fails, the photovoltaic systems, the energy storage batteries and the electric vehicles on the first direct current positive bus 411 and the second direct current positive bus 421 supply power to the alternating current loads through the DC/AC converter.

As shown in fig. 5 and fig. 6, the dc bus system 500 and the dc bus system 600 are dual power supply systems, and the dc bus system 500 shown in fig. 5 is used for illustration. The dc bus system 500 includes a first grid 531, a second grid 532, a first double-split transformer 541, a second double-split transformer 542, a first subsystem 510 and a second subsystem 520 with the same layout and symmetrical distribution, wherein one end of the first subsystem 510 and one end of the second subsystem 520 are respectively connected to the first double-split transformer 541 through a first switch 551 to obtain power from the first grid 531 side, and the other end of the first subsystem 510 and the other end of the second subsystem 520 are respectively connected to the second double-split transformer 542 through a fourth switch 552 to obtain power from the second grid 532 side. When the fourth switch 552 is opened and the first switch 551 is closed, power is supplied to the first subsystem 510 and the second subsystem 520 by the first power grid 531; when the first switch 551 is opened and the fourth switch 552 is closed, the second grid 532 supplies power to the first subsystem 510 and the second subsystem 520, so that the direct current bus system 500 can always maintain normal and stable operation. Of course, there may be more than one power source for supplying power to the dc bus system 500, and the present invention is not limited to the structure shown in fig. 5.

A second switch 514 is respectively arranged at two ends of the first ac bus 513, and a third switch 524 is respectively arranged at two ends of the second ac bus 523, and is used for selecting whether to supply power to the ac loads on the first ac bus 513 and the second ac bus 523 or selecting the first power grid 531 or the second power grid 532 to supply power to the ac loads.

According to the invention, the photovoltaic system, the energy storage battery, the electric automobile and other direct current loads are respectively designed on the plurality of direct current positive buses, so that systematic unified scheduling control can be realized, independent optimization control can be realized for the direct current positive buses, and the flexibility of the system is increased. As shown in fig. 7, the present invention further provides a control method of the dc bus system, which mainly includes the following steps:

step S1: collecting real-time data of each load on the direct current positive bus, and judging the working mode of the direct current positive bus;

the method comprises the steps of collecting real-time data of distributed power generation and direct-current loads on a direct-current positive bus, judging whether the direct-current positive bus works in a heavy-load mode or a light-load mode, and adjusting the power of the direct-current positive bus according to different working modes respectively to achieve the purpose of adjusting the power of the direct-current positive bus.

Step S2: if the direct current positive bus works in a heavy load mode, energy storage adjustment is carried out, so that the sum of the current vectors of the common direct current negative bus is zero, and power balance on the direct current positive buses is realized;

energy storage adjustment is performed according to the respective load real-time condition of the direct current positive bus and the power generation condition of the photovoltaic system, power balance on the direct current positive bus is achieved, the current vector of the public direct current negative bus is superposed to be zero, and therefore the loss of the direct current transmission line is halved.

Step S3: and if the direct current positive bus works in a light load mode, the first AC/DC converter or the second AC/DC converter is regulated to work intermittently.

When the first AC/DC converter and the second AC/DC converter connected with the main power grid work in a light load state, the system efficiency is extremely low, intermittent work of a rectifying end can be realized through flexible scheduling of system control and an energy storage device, the energy conversion efficiency is improved, a certain hiccup working mode can be adopted, the AC/DC converters on the first direct current positive bus and the second direct current positive bus are controlled to be closed and opened at intervals for a period of time, and in the opening stage of the first AC/DC converter or the second AC/DC converter, the positive bus and the negative bus supply power to a load together with the photovoltaic system; during the shutdown phase of the first AC/DC converter or the second AC/DC converter, the difference of the load energy is provided by the photovoltaic system and the energy storage device.

Because the power taking and rectifying power supplies of the plurality of direct current positive buses from the main power grid are mutually independent, and the distributed photovoltaic systems and the distributed energy storage batteries on the plurality of direct current positive buses are also mutually independent, the transfer of part of associated production loads among the plurality of direct current positive buses can be actively controlled through optimized production management, and more optimized operation of the system is realized.

Based on the direct current bus system provided by the invention, all the devices including the DC/AC converters and the AC/DC converters only bear half of the voltage of the power grid, but the voltage of the power grid is equivalent to a double-voltage bus of a conventional direct current bus system, so that the used power conversion devices are not limited by the voltage of the conventional devices at present.

It should be understood that the detailed description of the present invention is only for illustrating the present invention and is not limited by the technical solutions described in the embodiments of the present invention, and those skilled in the art should understand that the present invention can be modified or substituted equally to achieve the same technical effects; as long as the use requirements are met, the method is within the protection scope of the invention.

Claims (10)

1. A dc bus system, comprising:

at least one electrical grid;

the double-split transformer is connected with a power grid;

the first subsystem and the second subsystem are connected to the output end of the double-split transformer in parallel, and are distributed in the same layout and in a symmetrical mode;

the first subsystem comprises a first direct current positive bus, the second subsystem comprises a second direct current positive bus, real-time voltages on the first direct current positive bus and the second direct current positive bus are equal in size and opposite in direction, the first subsystem and the second subsystem share a direct current negative bus, and the sum of current vectors of the first subsystem and the second subsystem on the direct current negative bus is zero.

2. The DC bus system of claim 1,

the first subsystem comprises a first AC/DC converter, the second subsystem comprises a second AC/DC converter, the input end of the first AC/DC converter is connected with one output end of the double-splitting transformer through a first switch, the input end of the second AC/DC converter is connected with the other output end of the double-splitting transformer through a first switch, the output end of the first AC/DC converter is connected with the first direct current positive bus, and the output end of the second AC/DC converter is connected with the second direct current positive bus.

3. The DC bus system of claim 2, wherein the first and second DC positive buses are each connected to an AC load via a DC/AC converter.

4. The DC bus system of claim 1, wherein the first and second positive DC buses are each connected to a DC load via a DC/DC converter.

5. The dc bus system of claim 1, wherein the first subsystem further comprises a first ac bus, the second subsystem further comprises a second ac bus, the first ac bus and the second ac bus are respectively connected to the double split transformer through a first switch, and at least 1 ac load is connected to the first ac bus and the second ac bus.

6. The DC bus system of claim 5, wherein the first DC positive bus is connected to the AC load on the first AC bus via a DC/AC converter, and the second DC positive bus is connected to the AC load on the second AC bus via a DC/AC converter.

7. The dc bus system of claim 5, wherein a second switch is disposed between the first ac bus and the first switch, and a third switch is disposed between the second ac bus and the first switch.

8. The direct current bus system according to claim 1, comprising a first double-split transformer, a second double-split transformer, a first power grid and a second power grid, wherein the first double-split transformer is connected with the first power grid, the second double-split transformer is connected with the second power grid, one end of the first subsystem and one end of the second subsystem are connected to the output end of the first double-split transformer, and the other end of the first subsystem and the other end of the second subsystem are connected to the output end of the second double-split transformer.

9. A control method of a dc bus system, applied to the dc bus system according to any one of claims 1 to 8, wherein the control method comprises the steps of:

step S1: acquiring real-time load data on a direct current positive bus, and judging the working mode of the direct current positive bus;

step S2: if the direct current positive bus works in a heavy load mode, energy storage adjustment is carried out, so that the sum of the current vectors of the common direct current negative bus is zero, and power balance on the direct current positive buses is realized;

step S3: and if the direct current positive bus works in a light load mode, the first AC/DC converter or the second AC/DC converter is regulated to work intermittently.

10. The method for controlling a dc bus system according to claim 9, wherein the step S3 further includes:

step 31: in the starting stage of the first AC/DC converter or the second AC/DC converter, the positive bus and the negative bus supply power to the load together with the photovoltaic system;

step 32: during the shutdown phase of the first AC/DC converter or the second AC/DC converter, the difference of the load energy is provided by the photovoltaic system and the energy storage device.

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