CN110429635B - Commutation failure prediction method based on direct current finite time domain prediction - Google Patents

Abstract

The invention discloses a commutation failure prediction method based on direct current finite time domain prediction. The invention detects the direct current in real time after the system stably operatesWhen the change of the direct current voltage difference delta U and the derivative d delta U/dt of the direct current voltage difference delta U on two sides of the line rectification and inversion is larger than a preset threshold value, the critical value of the direct current change quantity is calculated, and an iterative function is constructed at the same time

Calculating direct current predicted value x by using Steffensen iterative algorithm_k. When the DC current predicted value x_kGreater than the critical DC current variation delta I_d ^*Then, a commutation failure prediction signal is sent. The method can realize the successful prediction of the first commutation failure without additionally increasing equipment or changing the topological structure of the current converter, and is easier to realize.

Description

Commutation failure prediction method based on direct current finite time domain prediction

Technical Field

The invention relates to a commutation failure prediction method for a high-voltage direct-current power transmission system, in particular to a commutation failure prediction method based on direct-current limited time domain prediction, and belongs to the technical field of operation and control of power systems.

Background

The high-voltage direct-current transmission is widely applied to alternating-current asynchronous networking and long-distance large-capacity transmission occasions in the global range by virtue of the advantages of long distance, large capacity, small loss, rapid and flexible power regulation and the like. Energy and load centers in China present a reverse distribution trend, so that the high-voltage direct-current transmission has a very wide application background in China.

The commutation failure is one of the most common faults in the high-voltage direct-current transmission system, and can cause the instantaneous interruption of the transmission power of the system, and meanwhile, if the control is improper, the continuous commutation failure can be caused, and finally, the direct-current system is locked, so that the safe and stable operation of the system is influenced. Therefore, the method for predicting commutation failure has important theoretical and engineering values.

At present, for the research on the phase commutation failure suppression technology, two means of changing a control strategy and changing a topological structure are mainly provided for the follow-up phase commutation failure, but the above means cannot realize the prevention and control of the phase commutation failure. The domestic research on the first commutation failure prediction control technology is still less, but a certain result is obtained, and the main obvious results are as follows: through a CFPREV technology for rapidly detecting faults of an alternating current system, a trigger delay angle change value is generated through a PI controller, the probability of occurrence of commutation failure is reduced, and the technology is applied to actual engineering at present; the predictive extinction angle control has a high response speed, and is used by more domestic projects adopting ABB technology, so that the predictive extinction angle control has a high response speed and can realize the predictive control of commutation failure. More researches indicate that the difference between the calculated extinction angle and the actual extinction angle is larger during the fault transient state, so that the prediction control effect is poor.

Therefore, how to accurately predict the occurrence of the commutation failure in the traditional high-voltage direct-current power transmission system is a problem to be solved urgently.

Disclosure of Invention

The invention aims to provide a commutation failure prediction method based on direct current limited time domain prediction.

In order to solve the technical problems, the invention adopts the technical scheme that:

a commutation failure prediction method based on direct current finite time domain prediction comprises the following steps:

step 1: detecting a voltage difference: after the system stably operates, detecting the direct current voltage difference delta U and the derivative d delta U/dt thereof on the rectification and inversion sides of the direct current line in real time, and turning to the step 2 when the change is larger than a preset threshold value, or turning to the step 1;

step 2: calculating a critical value of the direct current change quantity:

in the formula: n is the number of 6 pulsating current converters in the actual engineering; k is the transformation ratio of the converter transformer; gamma ray_minTaking a limit off angle of 7.2 degrees; x_cThe inverter phase-change reactance is used, and alpha is an inverter trigger angle; i is_d(alpha) is a direct current instantaneous value, delta U is a voltage difference between two rectification and inversion sides of a direct current line, and E is an effective value of an alternating current voltage on the inversion side;

and step 3: calculating the coefficient k₁To k is₅The specific calculation formula is as follows:

in the formula: r_dThe equivalent resistance value of the direct current line is L, the equivalent inductance value of the direct current line is L, and f is 50 Hz;

and 4, step 4: calculating a direct current predicted value:

constructing an iterative function

And a Steffensen iteration algorithm is used, and the iteration rule is as follows:

setting the initial value x of fall₀Setting the threshold value as 0₀When | z is satisfied_k－y_k|≤₀Jumping out of iteration; meanwhile, the operation times are limited to 3k +1 to 4000/80, namely k is less than or equal to 16.3;

and 5: and (3) commutation failure prediction: when the DC current predicted value x_kWith a critical direct current transformation quantity delta I_d0 ^*Existence of a relation x_k＞ΔI_d0 ^*Then, a commutation failure prediction signal is sent.

The technical effect obtained by adopting the technical scheme is as follows:

1. the method can realize the successful prediction of the first commutation failure, and overcomes the problem of difficult successful prediction of the first commutation failure;

2. the method considers the influence caused by the smoothing reactor and the change of the commutation angle during the fault transient state, the direct current prediction precision is higher, and the prediction effect of commutation failure is better;

3. the invention does not need to additionally increase equipment or change the topological structure of the converter, and is easier to realize.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a flow chart of the present invention;

FIG. 2 is a block diagram of a standard DC test system.

Detailed Description

Example 1:

a commutation failure prediction method based on direct current finite time domain prediction comprises the following steps:

step 1: detecting a voltage difference: after the system stably operates, detecting the direct current voltage difference delta U and the derivative d delta U/dt thereof on the rectification and inversion sides of the direct current line in real time, and turning to the step 2 when the change is larger than a preset threshold value, or turning to the step 1;

step 2: calculating a critical value of the direct current change quantity:

in the formula: n is the number of 6 pulsating current converters in the actual engineering; k is the transformation ratio of the converter transformer; gamma ray_minTaking a limit off angle of 7.2 degrees; x_cThe inverter phase-change reactance is used, and alpha is an inverter trigger angle; i is_d(alpha) is a direct current instantaneous value, delta U is a voltage difference between two rectification and inversion sides of a direct current line, and E is an effective value of an alternating current voltage on the inversion side;

and step 3: calculating the coefficient k₁To k is₅The specific calculation formula is as follows:

in the formula: r_dThe equivalent resistance value of the direct current line is L, the equivalent inductance value of the direct current line is L, and f is 50 Hz;

and 4, step 4: calculating a direct current predicted value:

constructing an iterative function

And a Steffensen iteration algorithm is used, and the iteration rule is as follows:

setting the initial value x of fall₀Setting the threshold value as 0₀When | z is satisfied_k－y_k|≤₀Jumping out of iteration; meanwhile, the operation times are limited to 3k +1 to 4000/80, namely k is less than or equal to 16.3;

and 5: and (3) commutation failure prediction: when the DC current predicted value x_kWith a critical direct current transformation quantity delta I_d0 ^*Existence of a relation x_k＞ΔI_d0 ^*Then, a commutation failure prediction signal is sent.

In the present embodiment, a standard dc test system is adopted, the standard dc test system is shown in fig. 2, and the units of the resistor, the capacitor and the inductor in fig. 2 are Ω and μ F, H, respectively. The earth faults with different fault severity degrees are set for the inversion side conversion bus, 1.3s faults occur, the faults last for 0.1s, and the predicted system response time under the resistive and inductive earth faults are respectively shown in a table 1 and a table 2.

TABLE 1

TABLE 2

Claims (1)

1. A commutation failure prediction method based on direct current finite time domain prediction is characterized in that: the method comprises the following steps:

step 1: detecting a voltage difference: after the system stably operates, detecting the direct current voltage difference delta U and the derivative d delta U/dt thereof on the rectification and inversion sides of the direct current line in real time, and turning to the step 2 when the change is larger than a preset threshold value, or turning to the step 1;

step 2: calculating a critical value of the direct current change quantity:

in the formula: n is the number of 6 pulsating current converters in the actual engineering; k is the transformation ratio of the converter transformer; gamma ray_minTaking a limit off angle of 7.2 degrees; x_cFor inverter conversionThe phase reactance, alpha is an inverter trigger angle; i is_d(alpha) is a direct current instantaneous value, delta U is a voltage difference between two rectification and inversion sides of a direct current line, and E is an effective value of an alternating current voltage on the inversion side;

and step 3: calculating the coefficient k₁To k is₅The specific calculation formula is as follows:

in the formula: r_dThe equivalent resistance value of the direct current line is L, the equivalent inductance value of the direct current line is L, and f is 50 Hz;

and 4, step 4: calculating a direct current predicted value:

constructing an iterative function

And a Steffensen iteration algorithm is used, and the iteration rule is as follows:

setting the initial value x of fall₀Setting the threshold value as 0₀When | z is satisfied_k－y_k|≤₀Jumping out of iteration; meanwhile, the operation times are limited to 3k +1 to 4000/80, namely k is less than or equal to 16.3;

and 5: and (3) commutation failure prediction: when the DC current predicted value x_kWith a critical direct current transformation quantity delta I_d0 ^*Existence of a relation x_k＞ΔI_d0 ^*Then, a commutation failure prediction signal is sent.

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