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Hybrid direct-current transmission topology structure and control method

A hybrid DC transmission and topology technology, applied in the direction of power transmission and AC network, can solve the problems of bipolar DC transmission system increasing system investment cost, only changing the direction of DC current, not changing, only changing voltage polarity, etc. , to achieve the effect of low loss, easy flow capacity and reduced impact

Active Publication Date: 2015-07-22
NR ELECTRIC CO LTD +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Since the traditional DC converters all use thyristor converters, the current direction cannot be changed, and only the voltage polarity can be changed when the power flow is reversed, while the voltage source converter can only change the direction of the DC current when the power flow is reversed, but not The polarity of the DC voltage, so the power flow of the mixed-terminal DC transmission system generally cannot be changed. If it needs to be changed, it is generally necessary to install relevant switching elements and change the polarity of the voltage source converter. Currently, it is generally used in each voltage source converter Corresponding switching elements are installed at the ends of the converters to achieve the purpose of changing their voltage polarity, such as figure 2 As shown, switch elements S1, S2, S3, and S4 are added to the positive and negative ends of VSC converter 1; switching elements S5, S6, S7, and S8 are added to the positive and negative ends of VSC converter 2, so Polar DC transmission system increases the system investment cost
In addition, there are currently methods that use a voltage source converter with a relatively complex topology and use related control strategies to realize the reversal of the voltage polarity at both ends of the voltage source converter, which not only increases the cost, but also complicates the control. , reducing the reliability of the system

Method used

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  • Hybrid direct-current transmission topology structure and control method

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0038] Embodiment 1: the whole power flow reversal process is as shown Figure 7 as shown,

[0039] Specifically include the following steps:

[0040] (1) Obtain the automatic power flow reversal start signal;

[0041] (2) Reduce the DC power of the positive and negative poles at a certain rate until the DC current of the two poles drops to the minimum current;

[0042] (3) After the two-pole DC current drops to the minimum current, issue a step-down command, and at the same time modify the per-unit value of the voltage reference value to k1, and the value range of k1 is 0 to 1;

[0043] (4) When the DC voltage of the two poles drops to the voltage reference value, the DC current of one pole is reduced to zero and the operation is stopped;

[0044] (5) Wait for 0 to 60 minutes after one pole of DC is out of operation, and then reduce the other pole's DC current to zero;

[0045] (6) After both poles of DC are out of service, disconnect the AC circuit breakers Sc and Sd on ...

Embodiment 2

[0049] Example 2: When the negative DC is out of operation, the relevant equipment in the converter station where the voltage source converter is located is overhauled, and the power flow reversal process is as follows when only the positive DC is running:

[0050] (1) Obtain the automatic power flow reversal start signal;

[0051] (2) Reduce the positive DC power at a certain rate until the positive DC current drops to the minimum current;

[0052] (3) After the positive DC current drops to the minimum current, issue a step-down command, and at the same time modify the per-unit value of the voltage reference value to k3, and the value range of k3 is 0 to 1;

[0053] (4) When the positive DC voltage drops to the voltage reference value, stop the positive DC;

[0054] (5) After the positive DC is out of service, disconnect the AC circuit breaker Sc on the primary side of the transformer connected to the voltage source converter, and disconnect the switches on the positive and ...

Embodiment 3

[0057] Embodiment 3: The power transmission from the AC grid connected to the thyristor converter to the AC grid connected to the thyristor converter needs to be changed from the AC grid connected to the thyristor converter to the voltage source converter. The AC power grid transmits power, and the entire power flow reversal process specifically includes the following steps:

[0058] (1) Obtain the automatic power flow reversal start signal;

[0059] (2) Reduce the DC power of the positive and negative poles at a certain rate until the DC current of the two poles drops to the minimum current;

[0060] (3) After the direct current of two poles drops to the minimum current, the direct current of one pole is reduced to zero to stop operation;

[0061] (4) Wait for 0 to 60 minutes after one pole of DC is out of operation, and then reduce the DC current of the other pole to zero for outage;

[0062] (5) After both poles of DC are out of service, disconnect the AC circuit breakers...

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Abstract

The invention discloses a hybrid direct-current transmission topology structure and a control method. The hybrid direct-current transmission topology structure is characterized in that two groups of thyristor converters are connected in series to form a first converter station, two groups of voltage source type converters are connected in series to form a second converter station, switch elements are respectively mounted at the same positions of the positive ends and the negative ends of the converters, in series connection, of the first converter station or the second converter station or the first converter station and the second converter station, and meanwhile, the same positions of the positive ends and the negative ends of the converters are in parallel connection and crossly connected to the opposite ends through one switch element respectively. The control method includes reducing direct-current power of a direct-current system to zero, and changing states of the switch elements to invert voltage polarity of the direct-current system, thereby achieving overall operation of two poles after inversion of the direct-current voltage polarity or achieving new two-pole direct-current operation by means of crossing of the converters in series connection of the converter stations at both ends. The system of the hybrid direct-current transmission topology structure has advantages of low manufacturing cost as the conventional direct-current transmission and control flexibility as the flexible direct-current transmission, and the like.

Description

technical field [0001] The invention relates to the field of hybrid direct current transmission, in particular to a hybrid direct current transmission topology and a control method. Background technique [0002] HVDC transmission systems can be divided into two types: traditional DC transmission systems (LCC-HVDC) based on thyristor technology; flexible HVDC systems based on fully controlled power electronic device technology (Flexible-HVDC). The traditional direct current transmission system (LCC-HVDC) has low cost, low loss, and mature operation technology. At present, most of the operating direct current transmission systems in the world are LCC-HVDC systems, but the traditional direct current transmission system (LCC-HVDC) exists The inverter side is prone to commutation failure, strong dependence on the AC system, absorbing a large amount of reactive power, and the converter station occupies a large area. The new generation of flexible direct current transmission syste...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02J3/36
CPCY02E60/60
Inventor 赵文强王永平王俊生
Owner NR ELECTRIC CO LTD
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