CN104330671B - Evaluation and analysis method of alternating-current tie line power fluctuation caused by impulse disturbance - Google Patents

Abstract

The invention provides an evaluation and analysis method of alternating-current tie line power fluctuation caused by impulse disturbance. The evaluation and analysis method comprises the steps of obtaining the interregional oscillation frequency and the interregional damping ratio of the oscillation modes of the power grids on the two sides of a tie line, obtaining the ratio of the inertia constants of the power grids on the two sides of the tie line, determining the maximum power value and the equivalent impulse time of the impulse disturbance, determining the maximum value of the alternating-current tie line power fluctuation caused by the impulse disturbance and the time of obtaining the maximum value of the power fluctuation, and evaluating the influence of the impulse disturbance on the alternating-current tie line. The evaluation and analysis method of the alternating-current tie line power fluctuation caused by the impulse disturbance is applicable to analyzing the tie line fluctuation circumstances in cases of faults such as direct-current commutation failure and direct-current restart, and helpful for the system analysts and the dispatching operators to analyze the characteristics of the power grids.

Description

An Evaluation and Analysis Method of AC Tie-line Power Fluctuation Caused by Impulse Disturbance

technical field

The invention relates to an analysis method, in particular to an evaluation and analysis method for AC tie line power fluctuations caused by impulse disturbances.

Background technique

Due to the uneven distribution of resources and energy in my country and the long distance between energy bases and load centers, DC transmission has been widely used in my country, forming a large-scale AC-DC interconnected power grid. Especially with the large-scale construction of UHV DC projects, the mutual influence between AC and DC systems is more obvious, and commutation failure is one of the common ones. The AC fault of the receiving end grid will cause the DC commutation failure, and the DC commutation failure will cause a short-term disturbance to the AC system, which may cause fluctuations in the AC tie line. Since the commutation failure lasts for a short time and returns to normal afterwards, it has little impact on the system itself. However, the power fluctuation of the AC tie line caused by commutation failure will have a great impact on the transmission capacity of the AC tie line. A similar problem also exists when the DC restart is successful. Therefore, how to accurately calculate the fluctuation of AC tie-lines caused by impulse disturbances such as commutation failure and DC restart is of great significance to guide the actual arrangement of tie-lines.

The invention patent with the application number of 201010187823.1 discloses a calculation method for the peak power fluctuation of the AC tie line of the interconnected power system in two major areas, and uses a second-order linear system time domain analysis related method to give the area tie line caused by step disturbances such as unit tripping. Calculation method of fluctuating power. However, no analysis is given on the magnitude of the tie-line fluctuations due to rapid recovery of impulse disturbances such as commutation failure and DC restart success. However, there is a big difference between the fluctuation mechanism of tie-line caused by impulse disturbance and the fluctuation mechanism of tie-line caused by step disturbance such as unit tripping and DC blocking. If the method provided by the above-mentioned patent is used directly to calculate the magnitude of the tie-line fluctuation caused by the impulse disturbance, the result is very different.

Contents of the invention

In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides an evaluation and analysis method for AC tie-line power fluctuations caused by impulse disturbances, which is applicable to the analysis of tie-line fluctuations under faults such as DC commutation failures and DC restarts. It is beneficial for system analysts and dispatching operators to analyze the characteristics of the power grid.

In order to realize the above-mentioned purpose of the invention, the present invention takes the following technical solutions:

The present invention provides a method for evaluating and analyzing AC tie line power fluctuations caused by impulse disturbances. The method includes the following steps:

Step 1: Obtain the inter-area oscillation frequency and inter-area damping ratio of the grid oscillation mode on both sides of the tie line;

Step 2: Obtain the ratio of the inertia constant of the grid on both sides of the AC tie line;

Step 3: Determine the maximum power value and equivalent impulse time of the impulse disturbance;

Step 4: Determine the maximum power fluctuation of the AC tie line caused by the impulse disturbance and the time to obtain the maximum power fluctuation;

Step 5: Evaluate the impact of the impulse disturbance on the AC tie-line.

In the step 1, the inter-area oscillation frequency and the inter-area damping ratio of the grid oscillation mode on both sides of the tie line are obtained according to the eigenvalue analysis method in the small disturbance theoretical analysis, or the PRONY analysis is performed on the actual power oscillation curve of the tie line when a disturbance occurs The inter-area oscillation frequency and the inter-area damping ratio of the grid oscillation mode on both sides of the tie line are obtained, and the inter-area oscillation frequency and the inter-area damping ratio are denoted by ω _d and ξ, respectively.

In the step 2, according to the generator parameters of the power grids on both sides of the tie line, the ratio of the inertia constants of the power grids on both sides of the tie line is obtained, expressed by H _Σ1 /H _Σ2 , where H _Σ1 and H _Σ2 are respectively the power grids on both sides of the tie line The total inertia constant of all units.

In the step 3, according to the impulse disturbance situation, the maximum power value of the impulse disturbance is obtained, represented by ΔP _max ;

The equivalent impulse time of impulse disturbance is represented by ΔT, which is:

Among them, ΔP and t are the instantaneous value and duration of the impulse disturbance, respectively.

In the step 4, according to the response characteristics of the second-order system under the short-term square wave disturbance, the maximum value of the power fluctuation of the AC tie line caused by the impulse disturbance and the time to obtain the maximum power fluctuation can be determined.

Described step 4 comprises the following steps:

(4-1) Since the square wave disturbance can be decomposed into positive step disturbance and negative step disturbance, according to the wave equation of the AC tie line subjected to the step disturbance, the wave equation of the square wave disturbance is obtained:

_Among them, h(t) is the _fluctuation function of AC tie line disturbed by square wave, ΔP _s is the size of square wave disturbance, Δt is the time of square wave disturbance; constant, ξ is the inter-area damping ratio, ω _n is the natural oscillation frequency, ω _d is the inter-area oscillation frequency, and β is the initial phase angle;

Since ΔT is much smaller than the interregional oscillation period and ξ is smaller than 0.15, is approximately 1, so formula (1) is simplified to:

Since the impulse time is much shorter than the inter-area oscillation period, formula (2) can be simplified as:

Multiple square wave disturbances are superimposed to form an impulse disturbance, ignoring the attenuation and phase difference between each square wave response, according to formula (3), the wave equation of the AC tie line caused by the impulse disturbance can be obtained:

Among them, H(t) is the fluctuation function of the AC tie line caused by the impulse disturbance, ΔP _max is the maximum power value of the impulse disturbance, and is the equivalent impulse time of the ΔT impulse disturbance;

(4-2) According to the wave equation of the AC tie-line caused by the impulse disturbance, the maximum power fluctuation of the AC tie-line caused by the impulse disturbance and the time to obtain the maximum power fluctuation are respectively expressed as:

Among them, H _max is the maximum power fluctuation of the AC tie-line caused by the impulse disturbance, and t _p is the time when the power fluctuation of the AC tie-line caused by the impulse disturbance reaches the maximum value.

In the step 5, the impact of the impulse disturbance on the AC tie line is evaluated according to the obtained maximum value of the power fluctuation of the AC tie line caused by the impulse disturbance and the time when the maximum power fluctuation is obtained, and the power fluctuation of the AC tie line caused by the impulse disturbance is The larger the maximum value, the greater the impact of the impulse disturbance on the AC tie line.

Compared with prior art, the beneficial effect of the present invention is:

The invention evaluates the impact of the impulse disturbance on the AC tie line by obtaining the maximum value of the power fluctuation of the AC tie line caused by the impulse disturbance and the time for obtaining the maximum value of the power fluctuation. It is suitable for fast and accurate analysis of tie-line fluctuations caused by impulse faults such as DC commutation failure and DC restart, and provides a basis for the arrangement of tie-line methods and the formulation of control measures, which is beneficial for system analysts and dispatchers to analyze the power grid characteristic.

Description of drawings

Fig. 1 is the flow chart of the evaluation and analysis method of AC tie line power fluctuation caused by impulse disturbance in the embodiment of the present invention;

Fig. 2 is a DC power waveform diagram when the phase commutation failure occurs when the external direct current of the Central China Power Grid is restored to the direct current according to the embodiment of the present invention;

Fig. 3 is a fluctuation waveform diagram (initial power has been subtracted) of the Changnan I line of the Central China-North China connection line during the commutation failure period in the embodiment of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings.

As shown in Fig. 1, the present invention provides a method for evaluating and analyzing AC tie line power fluctuations caused by impulse disturbances, the method comprising the following steps:

Step 1: Obtain the inter-area oscillation frequency and inter-area damping ratio of the grid oscillation mode on both sides of the tie line;

Step 2: Obtain the ratio of the inertia constant of the grid on both sides of the AC tie line;

Step 3: Determine the maximum power value and equivalent impulse time of the impulse disturbance;

Step 4: Determine the maximum power fluctuation of the AC tie line caused by the impulse disturbance and the time to obtain the maximum power fluctuation;

Step 5: Evaluate the impact of the impulse disturbance on the AC tie-line.

In the step 1, the inter-area oscillation frequency and the inter-area damping ratio of the grid oscillation mode on both sides of the tie line are obtained according to the eigenvalue analysis method in the small disturbance theoretical analysis, or the PRONY analysis is performed on the actual power oscillation curve of the tie line when a disturbance occurs The inter-area oscillation frequency and inter-area damping ratio of the grid oscillation mode on both sides of the tie line are obtained, and the inter-area oscillation frequency and the inter-area damping ratio are denoted by ω _d and ξ, respectively.

In the step 2, according to the generator parameters of the power grids on both sides of the tie line, the ratio of the inertia constants of the power grids on both sides of the tie line is obtained, expressed by H _Σ1 /H _Σ2 , where H _Σ1 and H _Σ2 are respectively the power grids on both sides of the tie line The total inertia constant of all units.

In the step 3, according to the impulse disturbance situation, the maximum power value of the impulse disturbance is obtained, represented by ΔP _max ;

The equivalent impulse time of impulse disturbance is represented by ΔT, which is:

Among them, ΔP and t are the instantaneous value and duration of the impulse disturbance, respectively.

In the step 4, according to the response characteristics of the second-order system under the short-term square wave disturbance, the maximum value of the power fluctuation of the AC tie line caused by the impulse disturbance and the time to obtain the maximum power fluctuation can be determined.

Described step 4 comprises the following steps:

(4-1) Since the square wave disturbance can be decomposed into positive step disturbance and negative step disturbance, according to the wave equation of the AC tie line subjected to the step disturbance, the wave equation of the square wave disturbance is obtained:

_Among them, h(t) is the _fluctuation function of AC tie line disturbed by square wave, ΔP _s is the size of square wave disturbance, Δt is the time of square wave disturbance; constant, ξ is the inter-area damping ratio, ω _n is the natural oscillation frequency, ω _d is the inter-area oscillation frequency, and β is the initial phase angle;

Since ΔT is much smaller than the interregional oscillation period and ξ is smaller than 0.15, is approximately 1, so formula (1) is simplified to:

Since the impulse time is much shorter than the inter-area oscillation period, formula (2) can be simplified as:

Multiple square wave disturbances are superimposed to form an impulse disturbance, ignoring the attenuation and phase difference between each square wave response, according to formula (3), the wave equation of the AC tie line caused by the impulse disturbance can be obtained:

Among them, H(t) is the fluctuation function of the AC tie line caused by the impulse disturbance, ΔP _max is the maximum power value of the impulse disturbance, and is the equivalent impulse time of the ΔT impulse disturbance;

(4-2) According to the wave equation of the AC tie-line caused by the impulse disturbance, the maximum power fluctuation of the AC tie-line caused by the impulse disturbance and the time to obtain the maximum power fluctuation are respectively expressed as:

Among them, H _max is the maximum power fluctuation of the AC tie-line caused by the impulse disturbance, and t _p is the time when the power fluctuation of the AC tie-line caused by the impulse disturbance reaches the maximum value.

In the step 5, the impact of the impulse disturbance on the AC tie line is evaluated according to the obtained maximum value of the power fluctuation of the AC tie line caused by the impulse disturbance and the time when the maximum power fluctuation is obtained, and the power fluctuation of the AC tie line caused by the impulse disturbance is The larger the maximum value, the greater the impact of the impulse disturbance on the AC tie line. In order to prevent the maximum power of the AC tie line from reaching the line stability limit, the actual power of the AC tie line during normal operation is arranged to be less than the difference between the line stability limit and the maximum power fluctuation of the AC tie line caused by impulse disturbance.

Example

When commutation failure occurs in Central China or North China DC, the DC system imposes an impulse disturbance on the AC network, and under the action of the impulse disturbance, the power of Changnan Line I of the Central China-North China connection line will fluctuate. The correctness of this method is verified by the magnitude of the fluctuation of the Changnan I line of the Central China-North China connection line when the commutation failure occurs in an actual UHV DC transmission from Central China to East China and back to DC.

(1) According to the analysis of small disturbance theory or the actual power oscillation curve of tie line when disturbance occurs, it can be obtained that the oscillation frequency between China and North China Power Grid is 0.183Hz, and the damping ratio is 0.081;

(2) According to the generator parameters of the power grids on both sides of the tie line, the ratio of the inertia constants of the two power grids can be obtained as 0.67:1;

(3) According to the commutation failure waveform, the maximum impulse power of the disturbance can be obtained as 5.4 million kilowatts, and the equivalent impulse time is 0.14 seconds;

(4) Adopting the inventive method can calculate the maximum fluctuation value of the tie line to be 460,000 kilowatts, and the time to obtain the maximum fluctuation value is 1.43 seconds. The actual Changnan I line maximum fluctuation value is 510,000 kilowatts, and the maximum fluctuation value time is 1.7 seconds, two The results are basically the same, which verifies the correctness of this method. If the method in the patent titled "Calculation Method for Peak Power Fluctuation of AC Tie Lines of Two Regional Interconnected Power Systems" is used to calculate the maximum fluctuation value of 5.74 million kilowatts, the time to obtain the maximum fluctuation value is 2.73 seconds, which is different from the actual fluctuation situation very big. It shows that the method provided by the patent of the present invention is suitable for the calculation of the fluctuation of the tie line caused by the impulse disturbance; while the method proposed by the patent titled "the calculation method of the peak value of the power fluctuation of the AC tie line of the two major regional interconnected power systems" is not applicable to the impulse disturbance. The calculation of tie line fluctuation caused by disturbance is only applicable to the calculation of tie line fluctuation caused by step disturbance. The transmission power of the tie line can be reasonably arranged according to the maximum fluctuation value of the tie line and the stability limit of the tie line.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those of ordinary skill in the art can still modify or equivalently replace the specific implementation methods of the present invention with reference to the above embodiments. Any modifications or equivalent replacements departing from the spirit and scope of the present invention are within the protection scope of the claims of the pending application of the present invention.

Claims (6)

1. A method for evaluating and analyzing AC tie line power fluctuations caused by impulse disturbances, characterized in that: the method comprises the following steps: Step 1: Obtain the inter-area oscillation frequency and inter-area damping ratio of the grid oscillation mode on both sides of the tie line; Step 2: Obtain the ratio of the inertia constant of the grid on both sides of the AC tie line; Step 3: Determine the maximum power value and equivalent impulse time of the impulse disturbance; Step 4: Determine the maximum power fluctuation of the AC tie line caused by the impulse disturbance and the time to obtain the maximum power fluctuation; Step 5: Assess the impact of impulse disturbances on AC tie-lines; Described step 4 comprises the following steps: (4-1) Since the square wave disturbance can be decomposed into positive step disturbance and negative step disturbance, according to the wave equation of the AC tie line subjected to the step disturbance, the wave equation of the square wave disturbance is obtained: $\begin{array}{c}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ _Among them, h(t) is the _fluctuation function of AC tie line disturbed by square wave, ΔP _s is the size of square wave disturbance, Δt is the time of square wave disturbance; constant, ξ is the inter-area damping ratio, ω _n is the natural oscillation frequency, ω _d is the inter-area oscillation frequency, and β is the initial phase angle; Since Δt is much smaller than the interregional oscillation period and ξ is smaller than 0.15, is approximately 1, so formula (1) is simplified to: $\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&ap;</span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ Since the impulse time is much shorter than the inter-area oscillation period, formula (2) can be simplified as: $\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&ap;</span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ Multiple square wave disturbances are superimposed to form an impulse disturbance, ignoring the attenuation and phase difference between each square wave response, according to formula (3), the wave equation of the AC tie line caused by the impulse disturbance can be obtained: $\begin{array}{c}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&ap;</span>\underset{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; t</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;T\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$ Among them, ΔP is the instantaneous value of the impulse disturbance, H(t) is the fluctuation function of the AC tie line caused by the impulse disturbance, ΔP _max is the maximum power value of the impulse disturbance, and ΔT is the equivalent impulse time of the impulse disturbance; (4-2) According to the wave equation of the AC tie-line caused by the impulse disturbance, the maximum power fluctuation of the AC tie-line caused by the impulse disturbance and the time to obtain the maximum power fluctuation are respectively expressed as: ${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; \&ap;</span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;T\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&xi;</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$ ${\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; T</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$ Among them, H _max is the maximum power fluctuation of the AC tie-line caused by the impulse disturbance, and t _p is the time when the power fluctuation of the AC tie-line caused by the impulse disturbance reaches the maximum value. 2. The method for evaluating and analyzing AC tie line power fluctuations caused by impulse disturbances according to claim 1, wherein in step 1, the two sides of the tie line are obtained according to the eigenvalue analysis method in the theoretical analysis of small disturbances. The inter-area oscillation frequency and inter-area damping ratio of the grid oscillation mode, or the PRONY analysis of the actual power oscillation curve of the tie line when a disturbance occurs, to obtain the inter-area oscillation frequency and inter-area damping ratio of the grid oscillation mode on both sides of the tie line, and the inter-area oscillation Frequency and interregional damping ratios are denoted by _ωd and ξ, respectively. 3. The method for evaluating and analyzing AC tie line power fluctuations caused by impulse disturbances according to claim 1, characterized in that: in said step 2, according to the generator parameters of the power grids on both sides of the tie line, the two sides of the tie line are obtained. The ratio of the inertia constant of the power grid is represented by H _Σ1 /H _Σ2 , where H _Σ1 and H _Σ2 are the total inertia constants of all units in the power grid on both sides of the tie line respectively. 4. The method for evaluating and analyzing the AC tie-line power fluctuation caused by the impulse disturbance according to claim 1, characterized in that: in the step 3, according to the impulse disturbance situation, the maximum power value of the impulse disturbance is obtained, using ΔP _max means; The equivalent impulse time of impulse disturbance is represented by ΔT, which is: $\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; t</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \backslash </span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; x</span>}}$ Among them, ΔP and t are the instantaneous value and duration of the impulse disturbance, respectively. 5. The method for evaluating and analyzing AC tie line power fluctuations caused by impulse disturbances according to claim 1, characterized in that: in step 4, according to the response characteristics of the second-order system under transient square wave disturbances, it can be determined The maximum value of the power fluctuation of the AC tie line caused by the impulse disturbance and the time to obtain the maximum value of the power fluctuation. 6. The method for evaluating and analyzing AC tie line power fluctuations caused by impulse disturbances according to claim 1, characterized in that: in step 5, according to the obtained maximum value of AC tie line power fluctuations caused by impulse disturbances and The time to obtain the maximum power fluctuation is used to evaluate the influence of the impulse disturbance on the AC tie-line. The greater the maximum power fluctuation of the AC tie-line caused by the impulse disturbance, the greater the impact of the impulse disturbance on the AC tie-line.