TWI737432B - Method of estimating frequency nadir after the loss of one generator in the power system - Google Patents

Abstract

The present invention relates to a method of estimating frequency nadir after the loss of one generator in the power system. In the estimating method, the data of the loss of one generator are collected to determine a relationship line between the maximum frequency deviation of the power system and the power unbalance ratio. A maximum frequency deviation corresponding to the power unbalance ratio of the power system is found according to the relationship line. A frequency nadir after the loss of one generator in the power system is calculated by the maximum frequency deviation and the nominal frequency. The number of power on generating units or output power of the generating units can be adjusted according to the estimated frequency nadir so that the frequency nadir of the power system remains higher than the threshold of tripping an under frequency load shedding after the loss of one largest generating unit of the power system. Thus, this method avoids the load shedding and ensure the reliability of the power system supply when the loss of one generator in the power system.

Description

Method for predicting the lowest frequency value after a power system trip event

The invention relates to a technology for evaluating the power supply status of a power system, in particular to a method for predicting the lowest frequency value of the power system.

When the generator set in the power system trips, the power supplied by the power system will be reduced, resulting in an imbalance between power supply and demand. At this time, the frequency of the mains power is also reduced accordingly. If the frequency of the mains is lower than a low-frequency unloading threshold, it must be unloaded. Number of power supply households.

Please refer to Figure 3, which is a typical frequency response diagram when the generator set in the power system trips. Point A in the figure represents the nominal frequency (60Hz), which is the frequency under normal power supply. Once the generator set trips, the supply When the load is short of power generation, the system frequency will drop accordingly; at this time, the inertial frequency response of the generator set and part of the primary frequency response (that is, the governor response) will try to prevent the frequency attenuation, so the system frequency will drop to point C in the figure. Pull back to the stable frequency at point B after the lowest frequency. It can be seen from the figure that from the nominal frequency point A to the lowest frequency point C is the maximum deviation value of the frequency of this generator set.

Traditional generator sets provide inertia for the power system. If the power system has a larger inertia, compared to a power system with a smaller inertia, the power system with a larger inertia will have a smaller maximum frequency deviation under the same imbalance between supply and demand. .

However, as the power system incorporates renewable energy sources (such as solar and wind power), when the penetration rate of renewable energy increases, the impact on the frequency control of the utility power will become greater. Due to the decoupling of renewable energy through power electronic equipment, solar energy and the latest wind turbine technology cannot provide inertia for the power system, resulting in a reduction in the net load of the power system when there is a large amount of solar and wind power generation during light load periods, and it is replaced by renewable energy The traditional generator set causes the inertia of the system to become smaller; therefore, when the generator set trips, a larger frequency deviation is more likely to occur; as shown in Figure 4, the online off-peak load provided by the power system with a larger frequency deviation is more likely to occur. The number of generators is small and contains high solar and wind power generation, resulting in a smaller system inertia in the power system. When the power system trips, the ability to prevent the system frequency from falling is reduced, not only its lowest frequency (59.519Hz<59.58) Hz) is lower and reaches its lowest frequency more quickly.

Therefore, as the proportion of renewable energy power supply gradually increases, it is easier to cause low-frequency unloading after the generator set trips, so it is necessary to further propose a response mechanism.

In view of the above-mentioned current power system incorporating renewable energy, when a generator trip event occurs, the problem of low frequency unloading may occur. The main purpose of the present invention is to provide a method for predicting the lowest frequency value after a power system trip event occurs.

The main technical means used to achieve the above purpose is to make the lowest frequency value prediction method after a trip event of the power system occurs. The method includes the following steps: (a) Collect multiple trip data when the generator set of a power system trips; (b) Based on the trip data, determine a relationship line between the maximum frequency deviation after a trip event in the power system and the proportion of trips; (c) Use the relationship line to find out an estimated maximum frequency deviation corresponding to the proportion of a trip of one of the generator sets in the current power system; and (d) Use a nominal frequency and the maximum deviation of the frequency Value, calculate the lowest frequency value after the generator set tripping of the current power system.

The present invention collects the trip data of the generator set of the power generation system, and then determines a relationship line between the maximum deviation value of the power system frequency and the trip ratio based on the data, and finds the current power system through the relationship line The maximum frequency deviation value corresponding to the proportion of a trip of a generator set is calculated with the nominal frequency to obtain the lowest frequency value after the current power system trips; in this way, the generator set can be dispatched based on this lowest frequency The number of power-on or output size keeps the lowest frequency value of the power generation system higher than the low-frequency unloading critical value of the system after a trip event occurs, so as to avoid unloading the load when a real trip event occurs, ensuring the reliability of the power supply of the power system.

Figure 1: A flow chart of the method for predicting the lowest frequency value after a trip event occurs in the power system of the present invention.

Fig. 2A: A diagram of the relationship between the maximum deviation of the system frequency and the proportion of machine trips according to the present invention.

Fig. 2B: A diagram of the relationship between the maximum frequency deviation of another system of the present invention and the percentage of machine trips.

Fig. 2C: A comparison diagram of a relationship line of Fig. 2A and Fig. 2C.

Figure 3: A typical frequency response diagram of an existing generator set when it trips.

Figure 4: Existing frequency response diagram after a trip event occurs with different total loads.

In the following, the present invention cooperates with the drawings to explain the technical content in detail, and provides actual data to verify the effectiveness of the method for predicting the lowest frequency value after a trip event of the power system of the present invention.

First, please refer to FIG. 1, which is a flowchart of the method for predicting the lowest frequency value after a trip event occurs in the power system of the present invention, which includes the following steps (a) to (d).

In step (a), collect multiple trip data when a generator set trips; in this embodiment, the trip data includes: trip amount (power), total load (power), and maximum frequency deviation Value; where the amount of tripping refers to the amount of power lost when the generator set trips.

In step (b), according to the trip data collected in step (a), a relationship line between the maximum frequency deviation of a power system and the trip ratio is determined; wherein the trip ratio is Is the ratio of the tripping amount to the total load; in this embodiment, the relationship line is obtained by regression analysis of the tripping data, as shown in Figure 2A, each point in the figure represents the tripping data (jumping The relationship between the proportion and the maximum deviation of the system frequency), where the total amount of renewable energy generation when each data event occurs exceeds 300MW. After regression analysis and calculation, the relationship line in the figure is obtained; at the same time, as shown in Figure 2B, the number of trips is also collected The trip data of renewable energy power generation less than 300MW at the time of the event can be seen from the relationship line in Figure 2A and Figure 2B. The relationship line is a linear straight line. When the trip is relatively large, the maximum deviation of the system frequency is also large. , So there is a high correlation between the proportion of tripping and the maximum deviation of the system frequency. Please refer to Figure 2C again. From the perspective of the same percentage of trips, the system frequency change amplitude of the relationship line in Figure 2A is larger than the system frequency change amplitude of the relationship line in Figure 2B. The frequency deviation corresponding to the 2A relationship line is -0.5063Hz, and the frequency deviation corresponding to the relationship line in Figure 2B is -0.457Hz, so it can be proved that the increase in renewable energy power generation will cause the system inertia to drop.

In step (c), a percentage of the current power system trips is obtained, and a corresponding estimated maximum frequency deviation value is found from the relationship line based on the current percentage of trips.

In step (d), a nominal frequency and the maximum deviation value of the frequency are used to calculate the lowest frequency value after the current power system trips. As shown in the following table, the multiple trip data in the table have the lowest frequency of the actual power system after tripping, and the lowest frequency of each trip data predicted according to steps (c) and (d). The rightmost column in the table is It is the error value between the lowest frequency of the power system after the actual trip and the predicted lowest frequency. The error value is quite low, which means that the present invention can accurately estimate the lowest frequency after obtaining the percentage of the trip; in this embodiment, the nominal frequency It is 60Hz. For example, if the current generation capacity of renewable energy incorporated in the power system is greater than 300MW, when the generator set trips, and the trip accounted for 4%, then after comparing the relationship line L1 in Figure 2C, the generator set’s The maximum frequency deviation value is -0.67, based on the nominal frequency 60Hz, and the nominal frequency 60Hz is added to the maximum frequency deviation value, and the predicted minimum frequency is 59.33Hz (60+(-0.67)=59.33) .

As the penetration rate of renewable energy is increasing year by year, in order to maintain the accuracy of predicting the lowest frequency of the power system after a trip event, the above step (a) sets a collection period. If the current collection period ends, then collect the next collection. The trip data that occurs in the cycle are updated; therefore, the trip data is collected according to the collection period, and the relationship line of step (b) can be updated regularly, so that the lowest frequency can be accurately and accurately corresponded afterwards.

It can be seen from the above description that the present invention, based on data collection, observation and analysis of trip events over many years, finds that there is a high correlation between the proportion of trips after the generator set trips and the maximum deviation of the system frequency. Therefore, through collection and Analyze the recent trip data of the generator set to generate a regression relationship line between the proportion of trips and the maximum deviation of the system frequency for subsequent estimation of the lowest system frequency when the generator set trips; in this way, the lowest frequency estimated by the present invention can be Allow power system dispatch operators to more directly understand potential frequency deviations, ensure the safety of system operation and dispatch in the context of high renewable energy penetration, and avoid tripping events that trigger low-frequency unloading relays, affecting users' power consumption, and improving power supply quality; For example, system dispatch operators can dispatch additional units based on the estimated minimum frequency of the power system after a trip event, so that the generator set can provide sufficient inertial support during normal operation. Recovery in deviation.

In addition, the estimated result of the lowest frequency of the power system after a trip event of the present invention can also assess whether the required frequency modulation backup capacity of the system is sufficient, and ensure that the system is stable in power supply when encountering a large disturbance event, and will not affect users. It uses electricity.

Furthermore, the estimated result of the lowest frequency of the power system after the occurrence of a trip event in the present invention is also used as an offline learning tool for system dispatch operators.

To sum up, with the increase in the penetration rate of renewable energy in the existing power system, the ability of the generator set to prevent the attenuation of the system frequency after the trip is reduced, which causes the trip event to trigger the occurrence of the low-frequency unloading relay event, which seriously affects the user's power consumption and improvement of power supply. Quality; therefore, the method for predicting the lowest frequency value after a trip event occurs in the power system of the present invention is aimed at estimating the lowest frequency of the power system after the generator set trips, allowing the system dispatcher to dispatch power generation based on the lowest frequency of the system after the trip The unit keeps the lowest frequency value after the system tripping higher than the low-frequency unloading critical value of the power system to ensure the reliability of the power supply of the power system.

The above are only the embodiments of the present invention and do not limit the present invention in any form. Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the relevant technical field, Without departing from the scope of the technical solution of the present invention, when the technical content disclosed above can be used to make slight changes or modification into equivalent embodiments with equivalent changes, but any content that does not depart from the technical solution of the present invention is based on the technical essence of the present invention Any simple modifications, equivalent changes and modifications made to the above embodiments still fall within the scope of the technical solution of the present invention.

Claims (10)

A method for predicting the lowest frequency value after a trip event occurs in a power system, including: (a) collecting multiple trip data when a generator set of a power system trips; (b) determining the power according to the trip data A relationship line between the maximum frequency deviation after a trip event in the system and the proportion of trips; (c) Use the relationship line to find out the corresponding line of a trip proportion of one of the generators in the current power system An estimated maximum frequency deviation value; and (d) using a nominal frequency and the maximum frequency deviation value to calculate the lowest frequency value of the current power system after the generator set has tripped. The method for predicting the minimum frequency value according to claim 1, wherein in the above step (a), a collection period is further set, and the trip data occurs during the collection period. The method for predicting the lowest frequency value according to claim 2, wherein in step (a) above, if the current collection period is over, then collect the trip data that occurred in the next collection period, and update the trip data. The method for predicting the lowest frequency value according to any one of claims 1 to 3, wherein in the above step (a), the trip data includes: trip amount (power), total load (power), and frequency The maximum deviation value. The method for predicting the lowest frequency value according to any one of claims 1 to 3, wherein in the above step (b), the reference line is obtained by calculating the trip data by regression analysis. The method for predicting the lowest frequency value according to claim 4, wherein in the above step (b), the reference line is obtained by calculating the trip data by regression analysis. The method for predicting the lowest frequency value according to claim 5, wherein in the above step (b), the reference line is a linear straight line. The method for predicting the lowest frequency value according to claim 6, wherein in the above step (b), the reference line is a linear straight line. The method for predicting the lowest frequency value according to any one of claims 1 to 3, wherein in the above step (d), the nominal frequency is 60 Hz. The method for predicting the lowest frequency value according to claim 8, wherein in the above step (d), the nominal frequency is 60 Hz.

Images