CN115842335A - New energy power system transient frequency maximum deviation prediction method based on measurement - Google Patents

Abstract

The invention discloses a method for predicting the maximum deviation of transient frequency of a new energy power system based on measurement, which comprises the following steps: length of initialization time window t _d Sampling start point t ₀ Sampling interval delta t and prediction precision epsilon, and making i =1; obtaining the node of each generator of the power system at t ₀ ,t ₀ +t _d ]Frequency measurement data f (t) in a data window, and inertia center frequency deviation delta f (t) and a frequency change rate ROOF (t) are calculated; fitting a second-order polynomial expression-t curve by using a least square method; calculating a second-order polynomial zero value, judging whether the zero is a real number solution, and if so, determining the result delta f _ext Put into solution space Δ f _max (i) If not, houseDiscarding the value; extending the data window length t _d ＝t _d + Δ t, let i = i +1, the iterative calculation is continued until the condition | Δ f is satisfied _max (i)‑Δf _max (i-1) less than or equal to epsilon, and jumping out of circulation; taking the last calculation result as a final calculation value, and determining a frequency maximum deviation predicted value delta f _max,est . The method can predict the maximum deviation of the transient frequency of the system after suffering from high-power shortage in real time on line only by measurement data without knowing specific system parameters.

Description

New energy power system transient frequency maximum deviation prediction method based on measurement

Technical Field

The invention belongs to the technical field of power system frequency stability assessment and control, and particularly relates to a method for predicting the maximum transient frequency deviation of a new energy power system based on measurement.

Background

The proportion of high-proportion renewable energy sources in an alternating current synchronous interconnected system is gradually increased, and meanwhile, the probability of occurrence of direct current blocking faults is increased due to rapid development of an extra-high voltage transmission project, so that low-frequency accidents of direct current fed into a receiving end power grid are easily caused. Under the action of the factors, the total inertia of the system is also continuously reduced, the anti-interference capability of the system is weakened, and the problem of safety and stability of the frequency of a large power grid is increasingly prominent. Transient frequency deviation is a key parameter for monitoring frequency stability, has a guiding decision-making effect on a series of subsequent frequency control measures, and is vital to accurately predicting the maximum frequency deviation under large disturbance to ensure stable operation of a power grid.

Currently, the common frequency lowest point prediction methods are mainly classified into three categories: full-state simulation method, artificial intelligence method and model method. The full-state simulation method can accurately describe the detailed dynamic process of the system frequency, but depends on the known of a large number of parameters, has low calculation speed and is difficult to apply on line; the artificial intelligence method can process the problems of nonlinearity, inaccurate physical model and the like, but the prediction precision of the method is related to a training mode and a sample; the simulation analysis speed of the frequency dynamic process can be improved to a certain extent by the model method, but the model method is difficult to adapt to the change of the system topology structure under the condition that the large-scale wind power is connected into the power grid.

Disclosure of Invention

In order to solve the problems in the prior art, the invention aims to provide a method for predicting the maximum transient frequency deviation of a new energy power system based on measurement.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for predicting the maximum deviation of transient frequency of a new energy power system based on measurement comprises the following specific steps:

step 1: length of initialization time window t _d Start of sampling time t ₀ Sampling time interval Δ t, prediction accuracy ∈ and let count parameter i =1;

step 2: obtaining time window t of each generator inertia center node of new energy power system ₀ ,t ₀ +t _d ]Frequency measurement data f (t) of the range;

and step 3: in the time window t ₀ ,t ₀ +t _d ]Within the range, calculating inertia center frequency offset delta f (t) = f (t) -f (t-delta t), and calculating a frequency change rate value ROOF (t) = delta f (t)/delta t;

and 4, step 4: in the time window [ t ] ₀ ,t ₀ +t _d ]RangeFitting a frequency change rate value ROOF (t) = a Δ f (t) by using a least square method ² + b Δ f (t) + c to obtain coefficient parameters a, b and c of the fitted second-order polynomial;

and 5: according to the second-order polynomial obtained by fitting, making the polynomial be zero, and calculating its zero value

Judging whether the solution is a real solution or not, and if the solution is a real solution, judging the result delta f _ext Put into solution space Δ f _max (i) Performing the following steps; if the real number solution is not the real number solution, discarding the calculation result; />

Step 6: judging whether the obtained solution satisfies | Delta f _max (i)-Δf _max If the (i-1) | is less than or equal to epsilon, if the (i-1) | is not less than epsilon, i = i +1, and the time window length t is prolonged _d ＝t _d + Δ t at [ t ₀ ,t ₀ +t _d ]Repeating the steps 2-6 until the constraint condition is met, and jumping out of the cycle;

and 7: the last calculation result delta f _max (i) And as a final prediction result, predicting the maximum frequency deviation delta f after the disturbance of the new energy power system _max,est 。

The method for predicting the maximum deviation of the transient frequency of the new energy power system based on measurement can predict the maximum deviation value of the frequency by only utilizing the second-order polynomial zero point of solution fitting under the condition that the specific system parameters such as the parameters and the disturbance of a synchronizer and the operating condition are not known. Therefore, the method can realize the online real-time prediction of the maximum deviation of the transient frequency under the large disturbance of the system only by using the measured data, reduces the calculated amount of the modeling process of the complex power system and the electromagnetic transient simulation, improves the calculation efficiency, and provides a reference basis for the implementation of the subsequent frequency control strategy.

Drawings

FIG. 1 is a flow chart of the prediction method of the present invention.

FIG. 2 is an example topology diagram of an IEEE-39 node system.

FIG. 3 is a plot of the frequency response of the system after a disturbance.

Detailed description of the invention

The invention is further illustrated below using example simulations.

As shown in fig. 1, the present invention relates to a method for predicting the maximum deviation of transient frequency of a new energy power system based on measurement, which comprises the following steps:

step 1: length of initialization time window t _d =3s, start of sampling time t ₀ =0s, sampling time interval Δ t =0.1s, prediction accuracy ∈ =0.01, and let count parameter i =1;

step 2: in the time window t ₀ ,t ₀ +t _d ]Within the range, acquiring frequency measurement data f (t) of each generator inertia center node of the new energy power system;

and step 3: in the time window t ₀ ,t ₀ +t _d ]Within the range, calculating a frequency offset amount Δ f (t) = f (t) -f (t- Δ t), and calculating a frequency change rate value ROCOF (t) = Δ f (t)/Δ t;

and 4, step 4: in the time window [ t ] ₀ ,t ₀ +t _d ]Within the range, fitting a frequency change rate value ROOF (t) = a Δ f (t) by using a least square method ² + b Δ f (t) + c to obtain coefficient parameters a, b and c of the fitted second-order polynomial;

and 5: according to the second-order polynomial obtained by fitting, making the polynomial be zero, and calculating its zero value

Judging whether the solution is a real solution or not, and if the solution is a real solution, judging the result delta f _ext Put into solution space Δ f _max (i) Performing the following steps; if the real number solution is not the real number solution, discarding the calculation result;

step 6: judging whether the obtained solution satisfies | Delta f _max (i)-Δf _max If not, i = i +1, and the time window is prolonged by t _d ＝t _d + Δ t at [ t ₀ ,t ₀ +t _d ]Repeating the steps 2-6 until the constraint condition is met, and jumping out of the cycle;

and 7: the last calculation result delta f _max (i) The maximum deviation of the predicted frequency is noted as Δ f as the final prediction result _max,est 。

Simulation example

In the present invention, simulation work was performed on DIgSILENT software, and a modified IEEE-39 node system was selected as a test system, and the system topology is shown in FIG. 2. And replacing the synchronous machine G7 with a double-fed wind driven generator DFIG and battery energy storage parallel device with the same capacity, and forming a coordination control strategy for the system frequency. The system rated frequency is 50Hz, the synchronous machine speed regulator mainly comprises an IEEEG1 type speed regulator and an IEEEG3 type speed regulator, the running wind speed of the fan is 10m/s, the rated power is 2MW, the energy storage rated capacity is 30MVA, and the new energy access proportion of the whole system is 11.48%. The simulated data were processed in MATLAB.

To verify the effectiveness of the method of the present invention, a prediction of the maximum deviation of the transient frequency of the system was performed for the conditions tested in the IEEE-39 system. The load 21 is stepped 80% at 10s, resulting in a power deficit of 219.2 MW.

Fig. 3 is a frequency response dynamic characteristic curve of a system after disturbance, and it can be seen that the fluctuation of frequency can be significantly reduced by using the concept of the inertia center frequency, which is very important for subsequent accurate prediction. The frequency falls to 49.6273Hz at maximum after the disturbance.

By adopting the prediction method provided by the invention, the maximum deviation value of the obtained frequency is 49.622Hz based on the measurement data of the figure 3 for prediction. In order to quantitatively analyze the prediction error, an error value is introduced, as shown in formula (1).

Wherein, Δ f _max,est The maximum frequency deviation value, Δ f, predicted by the method of the present invention _max,real The actual maximum deviation value after the frequency disturbance.

The specific error calculation is shown in table 1:

TABLE 1 comparison of predicted and actual value errors

The predicted maximum frequency deviation value is compared with an actual value, and the error is small, so that the effectiveness and the accuracy of the method for predicting the maximum transient frequency deviation of the new energy power system based on the measurement are proved.

According to the analysis of the above calculation examples, the maximum frequency deviation can be accurately estimated in real time under the condition that the system parameters of the new energy power system are not known by using the method for predicting the maximum transient frequency deviation based on measurement provided by the invention. The method is high in calculation efficiency and good in accuracy, and has important significance for frequency stability assessment and control of the new energy power system.

Claims (1)

1. A method for predicting the maximum deviation of transient frequency of a new energy power system based on measurement is characterized by comprising the following steps:

the method comprises the following specific steps:

step 1: length of initialization time window t _d Start of sampling time t ₀ Sampling time interval Δ t, prediction accuracy ∈ and let count parameter i =1;

step 2: acquiring time window t of each generator inertia center node of new energy power system ₀ ,t ₀ +t _d ]Frequency measurement data f (t) of the range;

and step 3: in the time window t ₀ ,t ₀ +t _d ]Within the range, calculating inertia center frequency offset delta f (t) = f (t) -f (t-delta t), and calculating a frequency change rate value ROOF (t) = delta f (t)/delta t;

and 4, step 4: in the time window [ t ] ₀ ,t ₀ +t _d ]Within the range, fitting a frequency change rate value ROOF (t) = a Δ f (t) by using a least square method ² + b Δ f (t) + c to obtain coefficient parameters a, b and c of the fitted second-order polynomial;

and 5: according to the second-order polynomial obtained by fitting, making the polynomial be zero, and calculating its zero value

Judging whether the real number solution is true or notNumber, then the result Δ f _ext Put into solution space Δ f _max (i) Performing the following steps; if the real number solution is not the real number solution, discarding the calculation result;

step 6: judging whether the obtained solution satisfies | delta f _max (i)-Δf _max The (i-1) | is less than or equal to epsilon, epsilon is the prediction precision, if the value is not satisfied, i = i +1, and the time window length t is prolonged _d ＝t _d + Δ t at [ t ₀ ,t ₀ +t _d ]Repeating the steps 2-6 until the constraint condition is met, and jumping out of the cycle;

and 7: the last calculation result delta f _max (i) And as a final prediction result, predicting the maximum frequency deviation delta f after the disturbance of the new energy power system _max,est 。

Images