A power supply structure for converting single-phase electricity into three-phase electricity

Abstract

The present invention discloses a power supply structure for converting single-phase electricity into three-phase electricity, and belongs to the technical field of power supply and distribution of electric power grid. It includes a transmission line, an isolation transformer, a power converter and a three-phase Dyn transformer; the transmission line is respectively connected to the R terminal of the input end of the power converter and the A terminal of the triangle winding of the three-phase Dyn transformer; the output end of the power converter is connected to the input end of the isolation transformer; the N terminal of the output end of the isolation transformer is connected to the C terminal of the triangle winding of the three-phase Dyn transformer, and the M terminal of the output end of the isolation transformer is connected to the transmission line; the A terminal of the triangle winding of the three-phase Dyn transformer is respectively connected to the transmission line and the M terminal of the output end of the isolation transformer; the S terminal of the output end of the power converter and the B terminal of the triangle winding of the three-phase Dyn transformer are respectively grounded; the star winding of the three-phase Dyn transformer is connected to a low-voltage distribution network with a grounded neutral point. It is suitable for power distribution system transformation and fault repair.

Description

Technical Field

[0001] The invention relates to the technical field of power supply and distribution of electric power grids. Background Art

[0002] In my country, users in the field of low-voltage power distribution generally use single-phase power supply. When users need to use three-phase power, they need to re-erect power lines, which is very troublesome and time-consuming. For some special places where power is needed, such as users who are geographically dispersed, it is more economical to erect two-phase transmission lines and connect three-phase Dyn transformers to users, which does not take up space, but some users need three-phase power. In particular, when users need to use three-phase power for a short time due to special reasons, and the time for erecting new three-phase lines does not allow, if the power quality of the power grid allows, it is relatively easy to provide three-phase power, which will have greater economic and social value.

[0003] In the power distribution system, electrical equipment suffers from various line failures due to long-term mechanical and electromagnetic forces, thermal effects, severe oxidation, poor contact, etc., which prevents the equipment from operating normally. In 2008, the Hunan power grid suffered a rare ice and snow disaster, with more than 60,000 poles falling and more than 40,000 lines breaking on 10kV distribution lines, and more than 300,000 poles falling and more than 300,000 lines breaking on lines below 10kV. Common reasons for line failure in the distribution network are: (1) loose wire joints, especially when copper and aluminum wires are connected, electrochemical corrosion occurs on the contact surface, which increases the contact resistance and heat. Due to the increase in heat, the contact resistance increases further, and this vicious cycle makes the copper-aluminum twisted joints inevitably burn out; (2) when installing a fuse, one phase of the fuse melts due to damage to one phase or inconsistent three-phase capacity; (3) the contact of a phase of the switch or starting device is burned, loose, or has poor contact; (4) a phase of the motor winding is broken or the joint is loose.

[0004] In rural power grids, users are geographically dispersed, and some homes may have small workshops or small workshops. The power system is sometimes equipped with three-phase lines, but because the poles are low, in severe weather conditions, one or two phases of the wires may be broken. In strong winds or rain, emergency repairs are very dangerous.

[0005] When the distribution network is in severe weather (such as strong winds and heavy rain) and there is a line break, if the power quality of the power grid permits, it can meet the emergency rescue operation of special or important three-phase loads. Power maintenance personnel can wait until the severe weather ends or eases before carrying out maintenance or emergency repairs, which will greatly improve users' satisfaction with power supply and prevent accidents and casualties among power maintenance personnel in severe weather conditions. Summary of the invention

[0006] The purpose of the present invention is to provide a power supply structure for converting single-phase electricity into three-phase electricity, which can effectively solve the technical problem of providing three-phase electricity when a single-phase user needs three-phase electricity or a three-phase user has one or two phases disconnected.

[0007] The object of the present invention is achieved through the following technical solutions: a power supply structure for converting single-phase electricity into three-phase electricity, comprising a transmission line L A , isolation transformer IT, power converter SC and three-phase Dyn transformer T, the transmission line L A The R terminal of the input end of the power converter SC and the A terminal of the triangle winding of the three-phase Dyn transformer T are connected respectively; the J terminal and K terminal of the output end of the power converter SC are connected to the P terminal and Q terminal of the input end of the isolation transformer IT respectively; the N terminal of the output end of the isolation transformer IT is connected to the C terminal of the triangle winding of the three-phase Dyn transformer T, and the M terminal of the output end of the isolation transformer IT is connected to the transmission line L A Connection: The A terminal of the triangle winding of the three-phase Dyn transformer T is connected to the transmission line L A , the M terminal of the output end of the isolation transformer IT is connected; the S terminal of the output end of the power converter SC and the B terminal of the triangle winding of the three-phase Dyn transformer T are respectively grounded to GND or through the return line L B Connection: Terminal a, terminal b, and terminal c of the star winding of the three-phase Dyn transformer T are connected to a low-voltage distribution network with a grounded neutral point.

[0008] The power converter SC includes a pulse width modulator CP, a first high power switch device SVG 1 And with the first high-power switching device SVG 1 The second largest power switch device in series SVG 2 and energy storage capacitor, the output end of the pulse width modulator CP is respectively connected to the first high power switching device SVG 1 and the second largest power switching device SVG 2 The control end is connected to the first high-power switching device SVG 1 The second largest power switching device SVG 2 Energy storage capacitors are connected in parallel.

[0009] The transmission line L A The current I is divided into current I 1 and current I 2 , where the current I 2 Connect to the power converter SC, the current I 1 They are connected to the isolation transformer IT and the three-phase Dyn transformer T respectively, and the current entering the three-phase Dyn transformer T is I A .

[0010] The current I 1The phase lags behind the transmission line L A The phase of the input voltage U is 30 degrees.

[0011] The second power switching device SVG of the power converter SC 2 The output voltage U MN The size is equal to the transmission line L A The input voltage U is large, and the second largest power switching device SVG of the power converter SC is 2 The output voltage U MN The phase lags behind the transmission line L A The phase of the input voltage U is 60 degrees.

[0012] The second high power switching device SVG 2 Output current I C Equal to the current I 1 , the second largest power switching device SVG 2 Output current I C Ahead of the transmission line L A The phase of the input voltage U is 30 degrees.

[0013] Compared with the prior art, the beneficial effects of the technology of the present invention are:

[0014] 1. The present invention can provide three-phase power supply in places where only single-phase transmission lines are set up in a low-voltage distribution network with a grounded neutral point. Since three-phase power supply is needed in an emergency and short-term manner, and time is not allowed to set up a new three-phase line, three-phase power supply can be provided if the power quality of the power grid permits.

[0015] 2. The present invention provides a three-phase power supply to meet the power needs of some special places. For example, if the users are geographically dispersed, a two-phase transmission line is set up and a three-phase Dyn transformer is connected to the users. This is more economical and does not take up space. However, some users need three-phase power.

[0016] 3. The present invention can provide three-phase power to three-phase users when two phases are disconnected, and the line can be repaired after the storm stops, thereby reducing the possibility of greater accidents caused by emergency situations.

[0017] Fourth, the present invention has good versatility and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the framework structure of the present invention.

[0019] Figure 2 It is a specific structural schematic diagram of the present invention.

[0020] Figure 3 It is a structural schematic diagram of the power converter of the present invention.

[0021] Figure 4 It is a schematic diagram of the specific structure of the second embodiment of the present invention.

[0022] Figure 5 It is a control flow chart of the pulse width modulator of the present invention. DETAILED DESCRIPTION

[0023] In order to better understand the creative idea of ​​the present invention, the working principle of the present invention is explained as follows: a pulse width modulator CP (pulse width modulator) is used to perform analog control on the analog circuit using the digital output of the microprocessor. The pulse width modulator can modulate the bias of the transistor base or the MOS tube gate according to the change of the corresponding load to achieve the change of the transistor or MOS tube conduction time, thereby achieving the change of the output of the switching regulated power supply. Assume that the transmission line L A The current is I, the transmission line L A The current I is divided into the first high power switch device SVG of the power converter SC. 1 The input current I 2 and branch current I 1 , current I 1 It is divided into two paths, one path enters the isolation transformer IT, and the other path enters the A terminal of the triangle winding of the three-phase Dyn transformer T. The input current is I A , the input current of the B terminal of the three-phase Dyn transformer T triangle winding is I B , the input current of the C terminal of the three-phase Dyn transformer T triangle winding is I C , Transmission Line L A The input voltage of the three-phase Dyn transformer T is U, and the input voltage of the C terminal of the star winding is U MN (also the output voltage of the isolation transformer IT or the second largest power switching device SVG of the power converter SC 2 output voltage).

[0024] The input current I in the power converter SC is controlled by the pulse width modulator CP. 2 , so that the shunted current I 1 The phase lags behind the transmission line L A The input voltage U has a phase of 30 degrees; the second largest power switch device SVG of the power converter SC is controlled by the pulse width modulator CP. 2 , making the second largest power switch device SVG of the power converter SC 2 The output voltage U MN The size is equal to the transmission line L A The input voltage U is large, and the second largest power switching device SVG of the power converter SC is 2 The output voltage U MN The phase lags behind the transmission line L AThe phase of the input voltage U is 60 degrees; the second largest power switching device SVG 2 Output current I C Equal to the current I 1 , the second largest power switching device SVG 2 Output current I C Ahead of the transmission line L A The input voltage U phase is 30 degrees (i.e., ahead of the isolation transformer U MN The phase is 90 degrees, acting as a capacitor); the a terminal, b terminal, and c terminal of the star winding of the three-phase Dyn transformer T are connected to the low-voltage distribution network with a grounded neutral point; thereby providing a three-phase symmetrical power supply to operate the load that requires three-phase power.

[0025] Embodiment 1

[0026] like Figure 1 and Figure 2 As shown, the embodiment of the present invention provides a power supply structure for converting single-phase electricity into three-phase electricity, including a transmission line L A , isolation transformer IT, power converter SC and three-phase Dyn transformer T; transmission line L A The R terminal of the input end of the power converter SC and the A terminal of the triangle winding of the three-phase Dyn transformer T are respectively connected; the R terminal and S terminal of the output end of the power converter SC are respectively connected to the P terminal and Q terminal of the input end of the isolation transformer IT; the N terminal of the output end of the isolation transformer IT is connected to the C terminal of the triangle winding of the three-phase Dyn transformer T, and the M terminal of the output end of the isolation transformer IT is connected to the transmission line L A Connection: The A terminal of the triangle winding of the three-phase Dyn transformer T is connected to the transmission line L A And the M terminal of the output end of the isolation transformer IT; the S terminal of the output end of the power converter SC and the B terminal of the triangle winding of the three-phase Dyn transformer T are grounded GND respectively; the a terminal, b terminal, and c terminal of the star winding of the three-phase Dyn transformer T are connected to the low-voltage distribution network with a grounded neutral point.

[0027] Continue as Figure 2 As shown, the power converter SC includes a pulse width modulator CP, a first high power switch device SVG 1 , and the second largest power switching device SVG 2 The output end of the pulse width modulator CP is connected to the first high power switch device SVG 1 and the second largest power switching device SVG 2 The energy storage capacitors are connected to the control end of the first high power switching device SVG 1 and the second largest power switching device SVG 2 in parallel.

[0028] In order to provide a three-phase symmetrical power supply and supply the load that requires three-phase power, in the embodiment of the present invention, the control flow of the pulse width modulator CP is as follows: Figure 5 As shown, the current I input into the power converter SC is controlled by the pulse width modulator CP. 2 , so that the shunted current I 1 The phase lags behind the transmission line L A The input voltage U has a phase of 30 degrees; the second largest power switch device SVG of the power converter SC is controlled by the pulse width modulator CP. 2 , making the second largest power switch device SVG of the power converter SC 2 The output voltage U MN The size is equal to the transmission line L A The input voltage U is large, and the second largest power switching device SVG of the power converter SC is 2 The output voltage U MN The phase lags behind the transmission line L A The phase of the input voltage U is 60 degrees; the second largest power switching device SVG 2 Output current I C Equal to the current I 1 , the second largest power switching device SVG 2 Output current I C Ahead of the transmission line L A The input voltage U is 30 degrees in phase (i.e. ahead of the isolation transformer U MN The phase is 90 degrees, acting as a capacitor).

[0029] like Figure 3 As shown, the first high-power switching device SVG 1 and the second largest power switching device SVG 2 The first high-power switching device SVG comprises four high-power transistors BG, each of which has a control electrode connected to the output end of the pulse width modulator CP; 1 and the second largest power switching device SVG 2 The emitter of any high-power transistor BG and the collector of any other high-power transistor BG are connected in series to form a high-power transistor group. In the embodiment of the present invention, the high-power transistor BG adopts an integrated gate-commutated thyristor IGCT, and insulated gate bipolar transistor IGBT can also be used. The first high-power switching device SVG 1 The series connection points of the emitter and the collector of each high-power transistor group constitute the first high-power switching device SVG 1 The R terminal and S terminal of the current input end; the second largest power switching device SVG 2The series connection points of the emitter and collector of each high-power transistor group constitute the second high-power switch device SVG 2 J and K terminals for current output.

[0030] Therefore, through the embodiment of the present invention, when the transmission line L of the neutral point grounded low voltage distribution network A In the case of severe weather (such as storms) when two-phase lines are disconnected or single-phase users use three-phase power, if the power quality of the power grid allows, the emergency rescue operation of special or important three-phase loads can be met. The power maintenance staff can set the structure described in the present invention at the two-phase line disconnection of the neutral point grounded low-voltage distribution network, so as to wait for the severe weather to end or ease before carrying out maintenance or emergency repairs. The present invention is an embodiment that is suitable for places where only single-phase transmission lines are erected. Since three-phase power is needed for a short-term emergency, and the time for erecting a new three-phase line does not allow, three-phase power can be provided to users if the power quality of the power grid allows.

[0031] Embodiment 2

[0032] like Figure 4 As shown, the embodiment of the present invention provides a power supply structure for converting single-phase electricity into three-phase electricity, including a transmission line L A , isolation transformer IT, power converter SC and three-phase Dyn transformer T; transmission line L A The R terminal of the input end of the power converter SC and the A terminal of the triangle winding of the three-phase Dyn transformer T are respectively connected; the R terminal and S terminal of the output end of the power converter SC are respectively connected to the P terminal and Q terminal of the input end of the isolation transformer IT; the N terminal of the output end of the isolation transformer IT is connected to the C terminal of the triangle winding of the three-phase Dyn transformer T, and the M terminal of the output end of the isolation transformer IT is connected to the transmission line L A Connection: The A terminal of the triangle winding of the three-phase Dyn transformer T is connected to the transmission line L A and the M terminal of the output end of the isolation transformer IT; the S terminal of the output end of the power converter SC and the B terminal of the triangle winding of the three-phase Dyn transformer T are grounded respectively; the a terminal, the b terminal and the c terminal of the star winding of the three-phase Dyn transformer T are connected to a low-voltage distribution network with a grounded neutral point.

[0033] The embodiment of the present invention is mainly different from the above-mentioned embodiment 1 in that: the S terminal of the output end of the power converter SC and the B terminal of the triangle winding of the three-phase Dyn transformer T are both connected through the return line L B The other structures and features are the same as those in the first embodiment, and will not be described in detail here. B and the transmission line L A A two-phase transmission line.

[0034] In summary, the present invention can not only solve the problem of single-phase users not having to re-erect lines when they need three-phase electricity, but also provide three-phase electricity to three-phase users when one or two phases are disconnected, thereby avoiding the risk of greater accidents due to emergency situations.

Claims

1. A power supply structure for converting single-phase electricity into three-phase electricity, comprising a transmission line L A , an isolation transformer IT, a power converter SC and a three-phase Dyn transformer T, characterized in that: The transmission line L A The R terminal of the input end of the power converter SC and the A terminal of the triangle winding of the three-phase Dyn transformer T are respectively connected; the J terminal and the K terminal of the output end of the power converter SC are respectively connected to the P terminal and the Q terminal of the input end of the isolation transformer IT; The N terminal of the isolation transformer IT output end is connected to the C terminal of the three-phase Dyn transformer T triangle winding, and the M terminal of the isolation transformer IT output end is connected to the transmission line L A Connection: The A terminal of the three-phase Dyn transformer T triangle winding is connected to the transmission line L A , connect the M terminal of the IT output end of the isolation transformer; The S terminal of the output end of the power converter SC and the B terminal of the triangle winding of the three-phase Dyn transformer T are grounded to GND or connected to the ground through the return line. L B Connection: The a terminal, b terminal and c terminal of the three-phase Dyn transformer T star winding are connected to the low-voltage distribution network with the neutral point grounded; The power converter SC includes a pulse width modulator CP, a first high-power switch device SVG1, and a second high-power switch device SVG2 connected in series with the first high-power switch device SVG1 and an energy storage capacitor. The output end of the pulse width modulator CP is connected to the control ends of the first high-power switch device SVG1 and the second high-power switch device SVG2 respectively, and the energy storage capacitor is connected in parallel between the first high-power switch device SVG1 and the second high-power switch device SVG2; the output voltage of the second high-power switch device SVG2 of the power converter SC U MN Equivalent in size to a power line L A Input voltage U Size, the output voltage of the second largest power switch device SVG2 of the power converter SC U MN The phase lags behind the transmission line L A Input voltage U The phase is 60 degrees.

2. A power supply structure for converting single-phase electricity into three-phase electricity according to claim 1, characterized in that: The transmission line L A Current I , after being divided into current I 1 and current I 2, where the current I 2 Connect to the power converter SC, current I 1 are connected to the isolation transformer IT and the three-phase Dyn transformer T respectively, and the current entering the three-phase Dyn transformer T is I A .

3. The power supply structure for converting single-phase electricity into three-phase electricity according to claim 2, characterized in that: The current I 1 has a phase lag behind the transmission line L A Input voltage U The phase is 30 degrees.

4. The power supply structure for converting single-phase electricity into three-phase electricity according to claim 1, characterized in that: The current output by the second high power switch device SVG2 is I C Equal to current I 1. The current output by the second largest power switch SVG2 I C Ahead of the transmission lines L A Input voltage U The phase is 30 degrees.

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