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Method for judging saturated harmonic instability of HVDC system converter transformer iron core

A technology of converter transformers and transformers, which is applied in the direction of instruments, measuring electric variables, measuring devices, etc., and can solve problems such as harmonic instability

Active Publication Date: 2014-04-16
SOUTH CHINA UNIV OF TECH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0018] according to image 3 , the harmonic transfer relationship in the case of converter transformer iron core saturation can be briefly described as follows: If there is a second harmonic voltage disturbance on the AC side of the converter, the disturbance voltage will cause an industrial disturbance on the DC side through the action of the converter switch. Frequency voltage, so as to generate power frequency harmonic current on the DC side; the DC power frequency current will generate positive sequence second harmonic current component and negative sequence DC current component on the AC side after being modulated by the converter; while the DC current flows through The converter transformer saturates the transformer core and generates a large number of harmonic currents of each order, including the positive-sequence second harmonic current; if the above-mentioned second harmonic currents act together on the positive-sequence second If the subharmonic voltage amplitude is greater than the original second disturbance harmonic voltage, the closed-loop positive feedback will cause harmonic instability

Method used

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  • Method for judging saturated harmonic instability of HVDC system converter transformer iron core
  • Method for judging saturated harmonic instability of HVDC system converter transformer iron core
  • Method for judging saturated harmonic instability of HVDC system converter transformer iron core

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Embodiment 1

[0116] In this embodiment, a method for judging harmonic instability of a converter transformer core saturation type in a HVDC system, in the high-voltage direct current (HVDC) system, the equivalent circuit of the AC-DC system is as follows Figure 4 As shown, the established simulation test system is as follows Figure 5 As shown, the values ​​of each parameter are as above, and the steps are as follows:

[0117] S1-1. According to the known power frequency voltage of the commutation bus with DC component I of DC current dc0 and trigger command angle α 0 , establish the switching function of voltage and current, and obtain the amplitude S of the power frequency sequence component of the switching function of voltage and current u1 and S i1 , specifically divided into the following four steps:

[0118] S11-1. According to the known power frequency voltage of the commutation bus with DC component I of DC current dc0 and trigger command angle α 0 , to calculate t...

Embodiment 2

[0133] The calculation steps of this embodiment are the same as those in Embodiment 1. In combination with the parameters in Table 3, λ=1.23 is finally obtained. If it is greater than 1, it is determined that the system is unstable; the corresponding DC line current waveform is as follows Figure 8 As shown in , it can be seen that the DC harmonics do not converge after the disturbance disappears, and the transformer is still in a saturated state.

Embodiment 3

[0135] The calculation steps of this embodiment are the same as those in Embodiment 1. In combination with the parameters in Table 3, λ=0.86 is finally obtained, which is less than 1. It is determined that the disturbance will decay with time, and the system will eventually stabilize; the corresponding DC line current waveform is as follows Figure 9 As shown in Figure 10, the waveform of the three-phase excitation current of the converter transformer when λ=0.86 is shown. It can be seen from the figure that with the attenuation of harmonics, the excitation current of the transformer decreases gradually, and finally the transformer changes from a saturated state to an unsaturated state. state.

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Abstract

The invention discloses a method for judging the saturated harmonic instability of an HVDC system converter transformer iron core. The method comprises the steps of S1, establishing a voltage current switching function according to power frequency voltage of a known conversion bus, direct current component of direct current and a trigger instruction angle and calculating a power frequency sequence component amplitude value of the voltage current switching function; S2, calculating a secondary equivalent harmonic impedance Zac2 of an alternating current system and a primary equivalent harmonic impedance Zac1 of a direct current system according to a alternating current / direct current equivalent circuit; S3, calculating a saturated harmonic unstable saturation stability factor lambda of a harmonic converter transformer; S4, finding that disturbance increases with the time and the system is unstable when the lambda is larger than 1, and the disturbance decreased with the time and the system finally tends to stability when the lambda is smaller than 1. In the method, the theoretical basis concept is clear, a computation expression is simple, parameters are easy to obtain, and the degree of the saturated harmonic instability of the converter transformer can be quantitatively accessed.

Description

technical field [0001] The invention relates to the technical field of electric power system protection, in particular to a method for judging the saturation type harmonic instability of an HVDC system converter transformer iron core. Background technique [0002] In current high-voltage direct current (HVDC) projects, the harmonic interaction between AC and DC systems may cause harmonic instability under certain conditions, that is, disturbances near the converter station cause harmonics to be difficult to attenuate or even amplify due to resonance The phenomenon. Harmonic instability will cause severe distortion of the commutation bus voltage, which may lead to difficulties in the operation of the DC system or even blockage, which will seriously affect the stable operation of the AC-DC system. The mechanism of harmonic instability in DC transmission is very complex, and the factors leading to harmonic instability are not unique, and the harmonic instability generated by t...

Claims

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Application Information

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IPC IPC(8): G01R31/00G01R23/16
Inventor 王钢李海锋刘俊磊梁远升钟庆汪隆君麦国浩
Owner SOUTH CHINA UNIV OF TECH
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