Power transmission line on-line ice melting device and control method thereof

Abstract

The invention discloses an on-line ice melting device for a power transmission line and a control method of the on-line ice melting device. According to an existing direct-current ice melting scheme, a power transmission line to be subjected to ice melting needs to be shut down firstly, then high-capacity direct current is injected into the line to be subjected to ice melting through a diode rectifier bridge, so that the line is heated, the purpose of ice melting is achieved, and online ice melting under the condition that the line is not shut down cannot be achieved. The online ice melting device for the power transmission line comprises a three-phase parallel branch, a single-phase parallel branch and an auxiliary ice melting branch, the three-phase parallel branch and the single-phase parallel branch are arranged at the head end of the ice melting line, the auxiliary ice melting branch is arranged at the tail end of the ice melting line, and online ice melting is achieved by controlling injection of zero-sequence current; the three-phase parallel branch and the single-phase parallel branch are interconnected at the DC side, and a voltage stabilizing capacitor is arranged between the three-phase parallel branch and the single-phase parallel branch to form a back-to-back DC system. According to the invention, on-line ice melting is realized, power consumers do not need to be transferred, lines do not need to be stopped, and normal use of electric equipment is not affected.

Description

Technical Field

[0001] The invention belongs to the technical field of power transmission line ice melting, in particular to an online ice melting device for a power transmission line and a control method thereof. Background Art

[0002] Conventional ice-melting devices require the shutdown of transmission lines, and distribution networks often have a single power supply line. If the power supply line needs to be melted, it is easy to cause power outages for users. In addition, since the distribution network is close to users, there are also problems such as low power quality and temporary voltage drops when melting ice.

[0003] CN104753015A discloses a transmission line de-icing device, including a transformer and a diode rectifier bridge, and also including a three-phase voltage source conversion and an AC output filter. The secondary winding of the transformer is respectively connected to the three-phase AC output end of the three-phase voltage source conversion and the AC output filter and the three AC input ends of the diode rectifier bridge. The three-phase voltage source conversion and the AC output filter are mainly composed of a three-phase voltage source conversion circuit and a three-phase filter circuit, which are used to convert the three-phase voltage source and compensate for the harmonic current generated by the diode rectifier bridge when the de-icing device operates in the de-icing mode, and operate in dynamic reactive power compensation when the de-icing is not performed, so as to improve the utilization rate of the de-icing transformer. The disadvantages of this patent document are that the device belongs to the existing DC de-icing scheme, that is, it is necessary to first shut down the transmission line to be de-iced, and then inject a large capacity DC current into the line to be de-iced through the diode rectifier bridge, so that the line is heated to achieve the purpose of de-icing, and it is impossible to achieve online de-icing under the condition that the line is not shut down. In addition, the diode rectifier bridge will also generate large harmonic currents, so it is necessary to configure a three-phase voltage source conversion circuit and a three-phase filter circuit to filter out the harmonics generated by the diode rectifier bridge to avoid affecting the power grid and users. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art and provide an online ice melting device for a transmission line and a control method thereof to realize online ice melting without transferring power users and shutting down lines, and without affecting the normal use of power equipment.

[0005] To this end, the present invention adopts the following technical solution.

[0006] In a first aspect, the present invention provides an online ice-melting device for a power transmission line, which includes a three-phase parallel branch, a single-phase parallel branch, and an auxiliary ice-melting branch;

[0007] The three-phase parallel branch and the single-phase parallel branch are arranged at the head end of the ice-melting line, and the auxiliary ice-melting branch is arranged at the end of the ice-melting line, and online ice-melting is realized by controlling the injection of zero-sequence current;

[0008] The three-phase parallel branch and the single-phase parallel branch are interconnected on the DC side, and a voltage stabilizing capacitor is arranged in the middle to form a back-to-back DC system. The three-phase parallel branch has a power quality control function.

[0009] Furthermore, the three-phase parallel branch is connected to the high-voltage end of the distribution transformer, and is connected by transformer step-down or direct connection.

[0010] Furthermore, the three-phase parallel branch is a three-phase voltage source rectifier converter.

[0011] Furthermore, the single-phase parallel branch is connected to the low-voltage end of the distribution transformer, and is connected to the neutral point of a Y-connected transformer or the neutral point of a Y-connected reactor.

[0012] Furthermore, the single-phase parallel branch is a single-phase voltage source inverter.

[0013] Furthermore, the AC side of the three-phase parallel branch is respectively connected to the three phases of the AC system; one end of the AC side of the single-phase parallel branch is connected to the neutral point of the Y-connected transformer or the neutral point of the Y-connected reactor, and the other end is grounded; a substation is configured with a set of three-phase parallel branches and single-phase parallel branches.

[0014] Furthermore, the auxiliary ice-melting branch is connected to the neutral point of a Y-connected transformer or a Y-connected reactor. If multiple outgoing lines of the same substation need to be ice-melted, a set of auxiliary ice-melting branches needs to be configured at the end of each ice-melting line.

[0015] Furthermore, the auxiliary ice-melting branch is a single-phase voltage source converter.

[0016] Furthermore, one end of the AC side of the auxiliary ice-melting branch is connected to the neutral point of the Y-connection transformer or the neutral point of the Y-connection reactor, and the other end is grounded; a voltage-stabilizing capacitor is provided on the DC side of the auxiliary ice-melting branch.

[0017] In a second aspect, the present invention provides a control method for the above-mentioned online ice melting device for a power transmission line, which comprises:

[0018] 1) Open the bypass switch CB2 of the starting resistor, close the charging switch CB1, and charge the three-phase parallel branch. The starting resistor is connected in series with the charging switch CB1;

[0019] 2) After the voltage of the voltage-stabilizing capacitor between the three-phase parallel branch and the single-phase parallel branch is stabilized, the bypass switch CB2 of the starting resistor is closed;

[0020] 3) After the voltage of the voltage-stabilizing capacitor between the three-phase parallel branch and the single-phase parallel branch is stable, unlock the three-phase parallel branch to control the DC voltage; the active power control mode of the three-phase parallel branch is fixed DC voltage;

[0021] 4) After the DC voltage is stabilized, the power quality control mode of the three-phase parallel branch is set. The voltage and current signals on the high-voltage side of the Y-connection transformer are detected in real time, and the harmonic voltage and harmonic current instructions that need to be compensated are obtained through fast Fourier algorithm analysis, thereby controlling the fully controlled power devices of the three-phase parallel branch to output the required harmonic current;

[0022] 5) Unlock the single-phase parallel branch and slowly increase the voltage, and unlock the auxiliary ice-melting branch after the stable capacitor on the DC side of the auxiliary ice-melting branch is powered;

[0023] 6) The single-phase parallel branch controls the AC side to inject zero-sequence current to meet the ice melting requirements;

[0024] 7) The auxiliary ice-melting branch controls the stable capacitor voltage on its DC side to maintain a constant voltage.

[0025] The beneficial effects of the present invention are as follows: First, online ice melting is achieved without the need to transfer power users or shut down lines. The present invention injects zero-sequence current into the line to be ice-melted by effectively controlling the fully controlled device, thereby causing the line to heat up and achieving the purpose of ice melting. When the electrical equipment is in normal use, the fundamental current flows through it, and there is no zero-sequence current channel. Therefore, the injection of zero-sequence current will not affect the normal use of the electrical equipment. Second, active management of power quality issues in transmission lines is achieved. Through the power quality control mode of the three-phase parallel branch, the harmonic voltage and harmonic current of the line on the high-voltage side of the Y-connected transformer can be effectively controlled, thereby improving the utilization rate of the ice-melting device and realizing the integrated multiplexing of the two functions of "ice melting + electric energy direct current". BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the structure of an online ice melting device for power transmission lines of the present invention;

[0027] Figure 2 Another structural schematic diagram of the online ice melting device for power transmission lines of the present invention. DETAILED DESCRIPTION

[0028] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0029] Example 1

[0030] This embodiment is an online ice melting device for power transmission lines. Figure 1 As shown, it includes a three-phase parallel branch, a single-phase parallel branch and an auxiliary ice-melting branch, and the transmission line to be melted is between the single-phase parallel branch and the auxiliary current branch.

[0031] The three-phase parallel branch and the single-phase parallel branch are arranged at the head end of the ice-melting line, and the auxiliary ice-melting branch is arranged at the end of the ice-melting line. By controlling the injection of zero-sequence current, online ice melting is realized; the three-phase parallel branch and the single-phase parallel branch are interconnected on the DC side, and a voltage-stabilizing capacitor is arranged in the middle to form a back-to-back DC system. The three-phase parallel branch has a power quality control function.

[0032] The three-phase parallel branch is connected to the high-voltage end of the distribution transformer, and is connected by transformer step-down or direct connection. In this embodiment, the three-phase parallel branch uses a three-phase voltage source rectifier converter.

[0033] The single-phase parallel branch is connected to the low-voltage end of the distribution transformer and is connected to the neutral point of the Y-connection transformer. In this embodiment, the single-phase parallel branch uses a single-phase voltage source inverter.

[0034] The AC side of the three-phase parallel branch is respectively connected to the three phases of the AC system; one end of the AC side of the single-phase parallel branch is connected to the neutral point of the Y-connection transformer, and the other end is grounded; a substation is equipped with a set of three-phase parallel branches and single-phase parallel branches.

[0035] One end of the AC side of the auxiliary ice-melting branch is connected to the neutral point of the Y-connection transformer, and the other end is grounded; a voltage-stabilizing capacitor is provided on the DC side of the auxiliary ice-melting branch. If multiple outgoing lines of the same substation need to be de-iced, a set of auxiliary ice-melting branches needs to be configured at the end of each de-icing line. In this embodiment, the auxiliary ice-melting branch uses a single-phase voltage source converter.

[0036] Example 2

[0037] This embodiment is an online ice melting device for power transmission lines. Figure 2 As shown, it includes a three-phase parallel branch, a single-phase parallel branch and an auxiliary ice-melting branch, and the transmission line to be melted is between the single-phase parallel branch and the auxiliary current branch.

[0038] The three-phase parallel branch and the single-phase parallel branch are arranged at the head end of the ice-melting line, and the auxiliary ice-melting branch is arranged at the end of the ice-melting line. By controlling the injection of zero-sequence current, online ice melting is realized; the three-phase parallel branch and the single-phase parallel branch are interconnected on the DC side, and a voltage-stabilizing capacitor is arranged in the middle to form a back-to-back DC system. The three-phase parallel branch has a power quality control function.

[0039] The three-phase parallel branch is connected to the high-voltage end of the distribution transformer, and is connected by transformer step-down or direct connection. In this embodiment, the three-phase parallel branch uses a three-phase voltage source rectifier converter.

[0040] The single-phase parallel branch is connected to the low-voltage end of the distribution transformer and connected to the neutral point of the reactor with Y connection. In this embodiment, the single-phase parallel branch uses a single-phase voltage source inverter.

[0041] The AC side of the three-phase parallel branch is respectively connected to the three phases of the AC system; one end of the AC side of the single-phase parallel branch is connected to the neutral point of the Y-connected reactor, and the other end is grounded; a substation is equipped with a set of three-phase parallel branches and single-phase parallel branches.

[0042] One end of the AC side of the auxiliary ice-melting branch is connected to the neutral point of the Y-connected reactor, and the other end is grounded; a voltage-stabilizing capacitor is provided on the DC side of the auxiliary ice-melting branch. If multiple outgoing lines of the same substation need to be de-iced, a set of auxiliary ice-melting branches needs to be configured at the end of each de-icing line. In this embodiment, the auxiliary ice-melting branch uses a single-phase voltage source converter.

[0043] Example 3

[0044] This embodiment is a control method for the online ice melting device for power transmission lines described in Embodiment 1 and Embodiment 2, and the steps are as follows:

[0045] 1) Open the bypass switch CB2 of the starting resistor, close the charging switch CB1, and charge the three-phase parallel branch. The starting resistor is connected in series with the charging switch CB1;

[0046] 2) After the voltage of the voltage-stabilizing capacitor between the three-phase parallel branch and the single-phase parallel branch is stabilized, the bypass switch CB2 of the starting resistor is closed;

[0047] 3) After the voltage of the voltage-stabilizing capacitor between the three-phase parallel branch and the single-phase parallel branch is stable, unlock the three-phase parallel branch to control the DC voltage; the active power control mode of the three-phase parallel branch is fixed DC voltage;

[0048] 4) After the DC voltage is stabilized, the power quality control mode of the three-phase parallel branch is set. The voltage and current signals on the high-voltage side of the Y-connection transformer are detected in real time, and the harmonic voltage and harmonic current instructions that need to be compensated are obtained through fast Fourier algorithm analysis, thereby controlling the fully controlled power devices of the three-phase parallel branch to output the required harmonic current, that is, realizing the power quality control function of the three-phase parallel branch;

[0049] 5) Unlock the single-phase parallel branch and slowly increase the voltage, and unlock the auxiliary ice-melting branch after the stable capacitor on the DC side of the auxiliary ice-melting branch is powered;

[0050] 6) The single-phase parallel branch controls the AC side to inject zero-sequence current to meet the ice melting requirements;

[0051] 7) The auxiliary ice-melting branch controls the stable capacitor voltage on its DC side to maintain a constant voltage.

[0052] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. An online ice melting device for a power transmission line, characterized in that: It includes three-phase parallel branch, single-phase parallel branch and auxiliary ice-melting branch; The three-phase parallel branch and the single-phase parallel branch are arranged at the head end of the ice-melting line, and the auxiliary ice-melting branch is arranged at the end of the ice-melting line; The three-phase parallel branch and the single-phase parallel branch are interconnected on the DC side, and a voltage stabilizing capacitor is arranged in the middle to form a back-to-back DC system.

2. The online ice melting device for power transmission lines according to claim 1, characterized in that: The three-phase parallel branch is connected to the high-voltage end of the distribution transformer, and is connected by transformer step-down or direct connection.

3. The online ice melting device for power transmission lines according to claim 2, characterized in that: The three-phase parallel branch is a three-phase voltage source type rectifier converter.

4. The online ice melting device for power transmission lines according to claim 1, characterized in that: The single-phase parallel branch is connected to the low-voltage end of the distribution transformer, and is connected to the neutral point of the Y-connection transformer or the neutral point of the Y-connection reactor.

5. The online ice melting device for power transmission lines according to claim 4, characterized in that: The single-phase parallel branch is a single-phase voltage source inverter.

6. The online ice melting device for power transmission lines according to claim 1, characterized in that: The AC side of the three-phase parallel branch is respectively connected to the three phases of the AC system; one end of the AC side of the single-phase parallel branch is connected to the neutral point of the Y-connected transformer or the neutral point of the Y-connected reactor, and the other end is grounded; a substation is equipped with a set of three-phase parallel branches and single-phase parallel branches.

7. The online ice melting device for power transmission lines according to claim 1, characterized in that: The auxiliary ice-melting branch is connected to the neutral point of a Y-connected transformer or a Y-connected reactor. If multiple outgoing lines of the same substation need to be de-iced, an auxiliary ice-melting branch needs to be configured at the end of each de-icing line.

8. The online ice melting device for power transmission lines according to claim 1, characterized in that: The auxiliary ice-melting branch is a single-phase voltage source converter.

9. The online ice melting device for power transmission lines according to claim 1, characterized in that: One end of the AC side of the auxiliary ice-melting branch is connected to the neutral point of the Y-connection transformer or the neutral point of the Y-connection reactor, and the other end is grounded; a voltage-stabilizing capacitor is provided on the DC side of the auxiliary ice-melting branch.

10. The control method of the online ice melting device for power transmission lines according to any one of claims 1 to 9, characterized in that: include: 1) Open the bypass switch CB2 of the starting resistor, close the charging switch CB1, and charge the three-phase parallel branch. The starting resistor is connected in series with the charging switch CB1; 2) After the voltage of the voltage-stabilizing capacitor between the three-phase parallel branch and the single-phase parallel branch is stabilized, the bypass switch CB2 of the starting resistor is closed; 3) After the voltage of the voltage-stabilizing capacitor between the three-phase parallel branch and the single-phase parallel branch is stable, unlock the three-phase parallel branch to control the DC voltage; the active power control mode of the three-phase parallel branch is fixed DC voltage; 4) After the DC voltage is stabilized, the power quality control mode of the three-phase parallel branch is set. The voltage and current signals on the high-voltage side of the Y-connection transformer are detected in real time, and the harmonic voltage and harmonic current instructions that need to be compensated are obtained through fast Fourier algorithm analysis, thereby controlling the fully controlled power devices of the three-phase parallel branch to output the required harmonic current; 5) Unlock the single-phase parallel branch and slowly increase the voltage, and unlock the auxiliary ice-melting branch after the stable capacitor on the DC side of the auxiliary ice-melting branch is powered; 6) The single-phase parallel branch controls the AC side to inject zero-sequence current to meet the ice melting requirements; 7) The auxiliary ice-melting branch controls the stable capacitor voltage on its DC side to maintain a constant voltage.

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