A combined single-phase electricity to three-phase electricity system

Abstract

The present invention discloses a combined single-phase power to three-phase power system, which relates to the technical field of power supply and distribution of electric power grids. The M terminal and the N terminal of the output end of the isolation transformer IT are respectively connected to the R terminal and the S terminal of the input end of the three-port power converter SC; the B terminal of the star winding of the three-phase transformer T is connected to the J2 terminal of the output end of the three-port power converter SC, and the C terminal of the star winding of the three-phase transformer T is connected to the J1 terminal of the output end of the three-port power converter SC; the center point of the star winding of the three-phase transformer T is respectively connected to the K1 terminal and the K2 terminal of the output end of the three-port power converter SC; the Q terminal of the isolation transformer IT is connected to the return line L B Connection, the a terminal, b terminal and c terminal of the three-phase transformer T triangle winding are connected to the low-voltage distribution network with grounded neutral point.

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 single-phase 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 a new three-phase line does not allow it, if the power quality of the power grid allows, it can be 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. A local 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 combined single-phase power to three-phase power system, which can effectively solve the technical problem when single-phase line users need three-phase power.

[0007] The object of the present invention is achieved through the following technical solutions: a combined single-phase power to three-phase power system, the system includes a transmission line L A , an isolation transformer IT, a three-port power converter SC and a three-phase transformer T, the A terminal of the star winding of the three-phase transformer T is connected to the transmission line L A Connect the input end of the isolation transformer IT to the transmission line L A The M terminal and the N terminal of the output end of the isolation transformer IT are respectively connected to the R terminal and the S terminal of the input end of the three-port power converter SC; the B terminal of the star winding of the three-phase transformer T is connected to the J2 terminal of the output end of the three-port power converter SC, and the C terminal of the star winding of the three-phase transformer T is connected to the J1 terminal of the output end of the three-port power converter SC; the center point of the star winding of the three-phase transformer T is respectively connected to the K1 terminal and the K2 terminal of the output end of the three-port power converter SC; the Q terminal of the input end of the isolation transformer IT is connected to the return line L B Connection, the a terminal, b terminal and c terminal of the three-phase transformer T triangle winding are connected to the low-voltage distribution network with grounded neutral point.

[0008] The three-port power converter SC includes a pulse width modulator CP, a first high-power switch device SVG1, a second high-power switch device SVG2 connected in series with the first high-power switch device SVG1, a third high-power switch device SVG3 connected in parallel with the second high-power switch device SVG2, and an energy storage capacitor CN. The output end of the pulse width modulator CP is respectively connected to the control ends of the first high-power switch device SVG1, the second high-power switch device SVG2, and the third high-power switch device SVG3. The energy storage capacitor CN is connected between the output terminal PP1 and the output terminal PN1 of the first high-power switch device SVG1; the output terminal PP1 of the first high-power switch device SVG1, the second high-power switch device SVG2, and the third high-power switch device SVG3 are connected in parallel. The input terminal PP2 of the high-power switching device SVG2 is connected to the input terminal PP3 of the third high-power switching device SVG3; the output terminal PN1 of the first high-power switching device SVG1, the input terminal PN2 of the second high-power switching device SVG2 and the input terminal PN3 of the third high-power switching device SVG3 are connected; the output terminal J1 of the second high-power switching device SVG2 and the output terminal J2 of the third high-power switching device SVG3 are respectively connected to the C terminal and the B terminal of the star winding of the three-phase transformer T; the output terminal K1 of the second high-power switching device SVG2 and the output terminal K2 of the third high-power switching device SVG3 are connected to the center point of the star winding of the three-phase transformer T.

[0009] The output voltage U of the second power switch device SVG2 of the three-port power converter SC is C The size is equal to the transmission line L A The input voltage U is large and the output voltage U of the second power switch device SVG2 of the three-port power converter SC is large. C Phase ahead of the transmission line L A The input voltage U has a phase of 120 degrees.

[0010] The output current I of the second high power switch device SVG2 C Size is equal to times the transmission line L A The current I of the second largest power switch device SVG2 is I C Phase ahead of the transmission line L A The phase of voltage U is 30 degrees.

[0011] The output voltage U of the third power switch device SVG3 of the three-port power converter SC B The size is equal to the transmission line L A The input voltage U is the output voltage U of the third power switch device SVG3 of the three-port power converter SC. B The phase lags behind the transmission line L A The input voltage U has a phase of 120 degrees.

[0012] The output current I of the third high power switch device SVG3 B Size is equal to times the transmission line L A The output current I of the third power switch device SVG3 is B The phase lags behind the transmission line L A The phase of 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, two-phase transmission lines can be set up and single-phase transformers can be used to connect 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 system described in Example 1 of the present invention.

[0019] Figure 2 It is a schematic diagram of the specific structure of the system described in Example 1 of the present invention.

[0020] Figure 3 It is a structural schematic diagram of the three-port power converter described in the first embodiment of the present invention.

[0021] Figure 4 It is a schematic diagram of the specific structure of the system described in Example 2 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 described as follows:

[0024] Assume that the transmission line L A The current of the three-phase transformer T is I, and the input current of the A terminal of the star winding is I A , the input current of the B terminal of the star winding of the three-phase transformer T is I B , the input current of the C terminal of the star winding of the three-phase transformer T is I C , Transmission Line L A The input voltage of the three-phase transformer T is U, and the input voltage of the A terminal of the star winding is U A The input voltage at the B terminal of the star winding of the three-phase transformer T is U B The input voltage of the C terminal of the star winding of the three-phase transformer T is U C .

[0025] The second high power switch SVG2 in the three-port power converter SC is controlled by the pulse width modulator CP so that the output voltage U C The size is equal to the transmission line L A The input voltage U and the output voltage U of the second power switch device SVG2 of the three-port power converter SC C The phase leads the transmission line L AThe input voltage U has a phase of 120 degrees; the second power switch device SVG2 in the three-port power converter SC is controlled by the pulse width modulator CP so that the output current I C Size is equal to times the transmission line L A The output current I of the second largest power switch device SVG2 is C Phase ahead of the transmission line L A The phase of the voltage U is 30 degrees (inductive reactive power); the third power switch device SVG3 in the three-port power converter SC is controlled by the pulse width modulator CP so that the output voltage U of the third power switch device SVG3 of the three-port power converter SC B The size is equal to the transmission line L A The input voltage U is the output voltage U of the third power switch device SVG3 of the three-port power converter SC. B The phase lags behind the transmission line L A The input voltage U has a phase of 120 degrees; the third power switch device SVG3 in the three-port power converter SC is controlled by the pulse width modulator CP so that the output current I B Size is equal to times the transmission line L A The output current I of the third power switch device SVG3 is B The phase lags behind the transmission line L A The phase of the voltage U is 30 degrees (capacitive reactive power); the triangle winding of the three-phase transformer T is connected to the low-voltage distribution network with the neutral point grounded, providing a three-phase symmetrical power supply for the load that requires three-phase power.

[0026] Embodiment 1

[0027] like Figure 1 As shown, the embodiment of the present invention provides a combined single-phase power to three-phase power system, wherein the system includes a transmission line L A , isolation transformer IT, three-port power converter SC and three-phase transformer T; the input end of the isolation transformer IT and the transmission line L A Connection; The three-phase transformer T star winding is connected to the three-port power converter SC and the transmission line L A Connection, the a terminal, b terminal and c terminal of the three-phase transformer T triangle winding are connected to the low-voltage distribution network with grounded neutral point.

[0028] like Figure 2 As shown, the P terminal of the input end of the isolation transformer IT is connected to the transmission line L AThe Q terminal of the isolation transformer IT is connected to the ground; the M terminal and the N terminal of the output end of the isolation transformer IT are connected to the R terminal and the S terminal of the input end of the corresponding three-port power converter SC respectively. The A terminal of the star winding of the three-phase transformer T is connected to the transmission line L A The B terminal of the star winding of the three-phase transformer T is connected to the J2 terminal of the output end of the three-port power converter SC, and the C terminal of the star winding of the three-phase transformer T is connected to the J1 terminal of the output end of the three-port power converter SC; the center point of the star winding of the three-phase transformer T is respectively connected to the K1 terminal and the K2 terminal of the output end of the three-port power converter SC.

[0029] like Figure 3 As shown, the three-port power converter SC includes a pulse width modulator CP, a first high power switch device SVG1, a second high power switch device SVG2 connected in series with the first high power switch device SVG1, a third high power switch device SVG3 connected in parallel with the second high power switch device SVG2, and an energy storage capacitor CN. The output end of the pulse width modulator CP is respectively connected to the control ends of the first high power switch device SVG1, the second high power switch device SVG2, and the third high power switch device SVG3. The energy storage capacitor CN is connected between the output terminal PP1 and the output terminal PN1 of the first high power switch device SVG1; the output terminal PP1 of the first high power switch device SVG1, the input terminal PP2 of the second high power switch device SVG2, and the input terminal PP3 of the third high power switch device SVG3 are connected; the output terminal PN1 of the first high power switch device SVG1, the input terminal PN2 of the second high power switch device SVG2, and the input terminal PN3 of the third high power switch device SVG3 are connected.

[0030] The first high-power switch device SVG1, the second high-power switch device SVG2 and the third high-power switch device SVG3 respectively include four high-power transistors BG, and the control electrode of each high-power transistor BG is connected to the output end of the pulse width modulator CP; the emitter of any high-power transistor BG of the first high-power switch device SVG1, the second high-power switch device SVG2 and the third high-power switch device SVG3 is connected in series with the collector of any other high-power transistor BG to form a group of high-power transistors. In the embodiment of the present invention, the high-power transistor BG adopts an integrated gate-commutated thyristor IGCT, and insulated gate bipolar transistors IGBT can also be used. The series connection point between the emitter and the collector of each group of high-power transistor groups of the first high-power switching device SVG1 respectively constitutes the R terminal and the S terminal of the current input end of the first high-power switching device SVG1; the series connection point between the emitter and the collector of each group of high-power transistor groups of the second high-power switching device SVG2 respectively constitutes the J1 terminal and the K1 terminal of the current output of the second high-power switching device SVG2; the series connection point between the emitter and the collector of each group of high-power transistor groups of the third high-power switching device SVG3 respectively constitutes the J2 terminal and the K2 terminal of the current output of the third high-power switching device SVG3.

[0031] 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 process is as follows: Figure 5 As shown, the output voltage U of the second power switch device SVG2 of the three-port power converter SC is C The size is equal to the transmission line L A The input voltage U is large and the output voltage U of the second power switch device SVG2 of the three-port power converter SC is large. C The phase leads the transmission line L A The input voltage U has a phase of 120 degrees. The output current I C Size is equal to times the transmission line L A The current I of the second largest power switch device SVG2 is I C The phase leads the transmission line L A The phase of the voltage U is 30 degrees. The output voltage U of the third power switch device SVG3 of the three-port power converter SC B The size is equal to the transmission line L A The input voltage U is the output voltage U of the third power switch device SVG3 of the three-port power converter SC. B The phase lags behind the transmission line L A The input voltage U has a phase of 120 degrees. The output current I B Size is equal to times the transmission line L A The output current I of the third power switch device SVG3 is B The phase lags behind the transmission line L A The phase of voltage U is 30 degrees.

[0032] Embodiment 2

[0033] like Figure 1 As shown, the embodiment of the present invention provides a combined single-phase power to three-phase power system, wherein the system includes a transmission line L A , isolation transformer IT, three-port power converter SC and three-phase transformer T; the input end of the isolation transformer IT and the transmission line L A Connection; The three-phase transformer T star winding is connected to the three-port power converter SC and the transmission line L A Connection, the a terminal, b terminal and c terminal of the three-phase transformer T triangle winding are connected to the low-voltage distribution network with grounded neutral point.

[0034] like Figure 4 As shown, the embodiment of the present invention is mainly different from the above-mentioned embodiment 1 in that: the Q terminal at the input end of the isolation transformer IT of the system is connected to 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 transmission line L A A two-phase transmission line.

[0035] 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 and heavy rain), when one phase of the line is disconnected, if the power quality of the power grid allows, the emergency rescue operation of special or important three-phase loads can be met, and the power maintenance staff can set the system described in the present invention at the place where the one-phase line of the neutral-grounded low-voltage distribution network is disconnected, so as to wait for the severe weather to end or ease before carrying out maintenance or emergency repairs. The embodiment of the present invention is mainly aimed at constructing a two-phase power transmission system to provide a three-phase power supply to meet the power needs of some special places. For example: users are geographically dispersed and two-phase transmission lines are set up. The single-phase power converter composed of the first high-power switching device SVG1, the second high-power switching device SVG2 and the third high-power switching device SVG3 provides voltage support through the DC energy storage capacitor, which is more economical and does not take up space, thereby meeting the user's three-phase power needs.

Claims

1. A combined single-phase power to three-phase power system, the system comprising a transmission line L A , isolation transformer IT, three-port power converter SC and three-phase transformer T, the A terminal of the star winding of the three-phase transformer T is connected to the transmission line L A Connect the P terminal of the input end of the isolation transformer IT to the transmission line L A Connect the Q terminal of the input end to ground or connect it to the return line L B connection; characterized in that: The M terminal and the N terminal of the output end of the isolation transformer IT are respectively connected to the R terminal and the S terminal of the input end of the three-port power converter SC; the B terminal of the star winding of the three-phase transformer T is connected to the J2 terminal of the output end of the three-port power converter SC, and the C terminal of the star winding of the three-phase transformer T is connected to the J1 terminal of the output end of the three-port power converter SC; the center point of the star winding of the three-phase transformer T is respectively connected to the K1 terminal and the K2 terminal of the output end of the three-port power converter SC; the a terminal, the b terminal and the c terminal of the triangle winding of the three-phase transformer T are connected to a low-voltage distribution network with a grounded neutral point.

2. A combined single-phase power to three-phase power system according to claim 1, characterized in that: The three-port power converter SC includes a pulse width modulator CP, a first high-power switch device SVG1, a second high-power switch device SVG2 connected in series with the first high-power switch device SVG1, a third high-power switch device SVG3 connected in parallel with the second high-power switch device SVG2, and an energy storage capacitor CN. The output end of the pulse width modulator CP is respectively connected to the control ends of the first high-power switch device SVG1, the second high-power switch device SVG2, and the third high-power switch device SVG3. The energy storage capacitor CN is connected between the output terminal PP1 and the output terminal PN1 of the first high-power switch device SVG1; the output terminals PP1 of the first high-power switch device SVG1, the second high-power switch device SVG2, and the third high-power switch device SVG3 are connected in parallel. The input terminal PP2 of the switching device SVG2 is connected to the input terminal PP3 of the third high power switching device SVG3; the output terminal PN1 of the first high power switching device SVG1, the input terminal PN2 of the second high power switching device SVG2 and the input terminal PN3 of the third high power switching device SVG3 are connected; the output terminal J1 of the second high power switching device SVG2 and the output terminal J2 of the third high power switching device SVG3 are respectively connected to the C terminal and the B terminal of the star winding of the three-phase transformer T; the output terminal K1 of the second high power switching device SVG2 and the output terminal K2 of the third high power switching device SVG3 are connected to the center point of the star winding of the three-phase transformer T.

3. A combined single-phase power to three-phase power system according to claim 2, characterized in that: The output voltage of the second power switch device SVG2 of the three-port power converter SC is U C Equivalent in size to a power line L A Input voltage U The output voltage of the second power switch device SVG2 of the three-port power converter SC is U C Phase ahead of the transmission line L A Input voltage U Phase 120 degrees.

4. A combined single-phase power to three-phase power system according to claim 2, characterized in that: The output current of the second high power switch device SVG2 I C Size is equal to Times the transmission line L A Current I The output current of the second largest power switch device SVG2 I C Phase ahead of the transmission line L A Voltage U The phase is 30 degrees.

5. A combined single-phase power to three-phase power system according to claim 2, characterized in that: The output voltage of the third power switch device SVG3 of the three-port power converter SC is U B Equivalent in size to a power line L A Input voltage U The output voltage of the third power switch device SVG3 of the three-port power converter SC is U B Phase lags behind the transmission line L A Input voltage U Phase 120 degrees.

6. A combined single-phase power to three-phase power system according to claim 2, characterized in that: The output current of the third high power switch device SVG3 I B Size is equal to Times the transmission line L A Current I The output current of the third largest power switch device SVG3 is I B Phase lags behind the transmission line L A Voltage U The phase is 30 degrees.

Images