CN114759584B - Frequency safety and stability judging method of power system considering energy storage inertia support - Google Patents
Frequency safety and stability judging method of power system considering energy storage inertia support Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
Abstract
The invention discloses a frequency safety and stability judging method of an electric power system considering energy storage inertia support, which comprises the steps of obtaining parameters of the electric power system to be analyzed before and after an energy storage device is added; calculating equivalent inertia time constants of the power grid systems to be analyzed before and after the energy storage device is added; calculating an equivalent inertia time constant of the power grid system to be analyzed after energy storage virtual inertia control is performed; calculating a critical value of an equivalent inertial time constant of the system; and calculating to obtain the safety margin of the inertia support analysis margin and the equivalent inertia time constant of the power grid system to be analyzed, and carrying out final frequency safety and stability judgment of the power grid system. The invention analyzes the supporting function of the energy storage to the inertia of the system after the energy storage is connected to a high-proportion new energy system based on the frequency change rate at the disturbance occurrence time and the energy storage virtual inertia control, and provides a quantitative analysis judging method so as to analyze the safety and stability of the system in the frequency transient response process; the method of the invention has high reliability, good safety and objectivity and science.
Description
Technical Field
The invention belongs to the field of electric automation, and particularly relates to a frequency safety and stability judging method of an electric power system considering energy storage inertia support.
Background
Along with the development of economic technology and the improvement of living standard of people, electric energy becomes an indispensable secondary energy source in the production and living of people, and brings endless convenience to the production and living of people. Therefore, ensuring stable and reliable supply of electric energy becomes one of the most important tasks of the electric power system.
In recent years, with the large-scale incorporation of renewable energy sources into the power grid, the safe and stable operation of power systems is greatly threatened. Synchronous generators in traditional power grids have good inertia and damping characteristics, and can maintain stable system frequency through inertial response. The large-scale renewable energy access not only reduces the equivalent inertia of the system, but also affects the safety and stability of the system frequency.
The power grid side energy storage device mainly faces to the regulation and control operation of a power grid; the power grid side energy storage technology is widely used for compensating virtual inertia and other links of the renewable energy system, and the operation characteristics of the renewable energy are greatly improved. The energy storage device has the characteristic of rapid charge and discharge, is flexible in configuration, and plays an important role in improving the controllable adjustability of renewable energy power generation. The quick response capability and flexible regulation and control characteristics of the energy storage device can make up for the defects of the traditional frequency modulation source. The energy storage device assists in grid frequency modulation and can effectively improve the frequency modulation characteristic of the system.
At present, although files are used for researching the frequency modulation effect of the power grid under different energy storage devices, the safety and stability in the transient response process of the system frequency are not analyzed and judged, and the related research and application of the energy storage devices are restricted to a certain extent.
Disclosure of Invention
The invention aims to provide a frequency safety and stability judging method for a power system, which is high in reliability, good in safety and objectively and scientifically considering energy storage inertia support.
The method for judging the frequency safety and stability of the power system considering the energy storage inertia support provided by the invention comprises the following steps:
s1, acquiring parameters of a power grid system to be analyzed before and after adding an energy storage device;
s2, calculating equivalent inertia time constants of the power grid system to be analyzed before and after the energy storage device is added;
s3, calculating an equivalent inertia time constant of the power grid system to be analyzed after energy storage virtual inertia control is performed;
s4, calculating to obtain a critical value of an equivalent inertia time constant of the system according to the maximum value of the frequency change rate of the power grid system to be analyzed;
s5, calculating to obtain an inertia support analysis margin of the energy storage system of the power grid system to be analyzed and an equivalent inertia time constant safety margin of the power grid system to be analyzed according to the calculation results of the steps S2-S4;
s6, according to the inertia margin and the safety margin calculated in the step S5, the final frequency safety stability judgment of the power system is carried out.
The step S2 of calculating the equivalent inertia time constant of the power grid system to be analyzed before and after adding the energy storage device specifically comprises the following steps:
before adding an energy storage device and considering new energy access, calculating an equivalent inertia time constant H of the power grid system to be analyzed by adopting the following formula T ：
Wherein N is the number of conventional units of the power grid system to be analyzed; h i,sys An equivalent inertial time constant provided for the ith unit for the whole system, and
H i is the inertia time constant of the ith unit, S i Is the capacity of the ith unit, S sys Capacity of a system general assembly machine;
after new energy is considered to be accessed, the equivalent inertial time constant H 'of the power grid system to be analyzed is calculated by adopting the following formula' T ：
H' T ＝H T (1-β)
Wherein beta is the permeability of new energy after being accessed into the power grid system to be analyzed.
The step S3 of calculating the equivalent inertia time constant of the power grid system to be analyzed after the energy storage virtual inertia control is carried out, specifically comprises the following steps:
the equivalent inertia time constant H of the power grid system to be analyzed after the energy storage virtual inertia control is obtained by adopting the following calculation formula W ：
In H' T To increase the equivalent inertia time constant H 'of the power grid system to be analyzed after the energy storage device' T The method comprises the steps of carrying out a first treatment on the surface of the K is an energy storage virtual inertia control parameter; s is S ESS Is the capacity of the energy storage device; s is S sys Is the capacity of the system assembly machine.
And step S4, calculating a critical value of an equivalent inertia time constant of the system according to the maximum value of the frequency change rate of the power grid system to be analyzed, wherein the method specifically comprises the following steps:
the critical value H of the equivalent inertial time constant of the system is calculated by adopting the following formula cr ：
In RoCoF max The maximum value of the frequency change rate of the power grid system to be analyzed; p (P) step And (5) the load disturbance of the power grid system to be analyzed.
The inertia margin of the power grid system to be analyzed in the step S5 is specifically calculated by adopting the following formula to obtain an inertia support analysis margin eta of the power grid system energy storage system to be analyzed to the system:
h in W The method comprises the steps of controlling the energy storage virtual inertia of a power grid system to be analyzed according to an equivalent inertia time constant; h'. T The equivalent inertial time constant of the power grid system to be analyzed after the new energy is accessed is considered; h cr Is the critical value of the equivalent inertial time constant of the power grid system to be analyzed.
The safety margin of the power grid system to be analyzed in step S5 is specifically calculated by the following formula to obtain an equivalent inertial time constant safety margin lambda of the power grid system to be analyzed:
h in W The method comprises the steps of controlling the energy storage virtual inertia of a power grid system to be analyzed according to an equivalent inertia time constant; h cr The method comprises the steps of determining a critical value of an equivalent inertial time constant of a power grid system to be analyzed; h T The equivalent inertia time constant of the power grid system to be analyzed before the energy storage device and the new energy are connected is increased.
And step S6, carrying out final frequency safety stability judgment of the power system according to the inertia margin and the safety margin calculated in the step S5, wherein the method specifically comprises the following steps of:
(1) According to the inertia support analysis margin eta, the following rule is adopted for judging:
if eta is more than 0, the transient response process of the power grid system to be analyzed is judged to be safe and stable;
if eta is more than-1 and less than 0, judging that the transient response process of the power grid system to be analyzed is unsafe and stable;
if eta is less than-1, judging the transient response process of the power grid system to be analyzed as safe and stable;
if eta= -1, judging the transient response process of the power grid system to be analyzed as critical safety and stability;
if eta=0, the energy storage has no inertia supporting effect on the system, if H' T -H cr The transient response process of the system is judged to be safe and stable if the transient response process is more than 0; if H' T -H cr < 0, the transient response process of the system is judged to be unsafe and stable;
(2) According to the inertia time constant safety margin lambda, the following rule is adopted for judging:
if lambda is more than 0, the equivalent inertia time constant margin of the power grid system to be analyzed is judged to be safe;
if lambda is less than 0, the equivalent inertia time constant margin of the power grid system to be analyzed is judged to be unsafe.
According to the frequency safety and stability judging method of the power system considering the energy storage inertia support, which is provided by the invention, the supporting effect of the energy storage on the system inertia after being connected into a high-proportion new energy system is analyzed based on the disturbance occurrence moment frequency change rate and the energy storage virtual inertia control, and a quantitative analysis judging method is provided, so that the safety and stability of the system in the frequency transient response process are analyzed; the method of the invention has high reliability, good safety and objectivity and science.
Drawings
FIG. 1 is a schematic flow chart of the method of the present invention.
Fig. 2 is a schematic diagram of a system frequency response curve of a system with or without energy storage participating in frequency adjustment according to an embodiment of the method of the present invention.
FIG. 3 is a schematic diagram of a system frequency response curve of an energy storage system virtual inertia control increased inertia time constant without superposition and superposition to a system equivalent inertia time constant according to an embodiment of the method of the present invention.
Fig. 4 is a schematic diagram of the system frequency response curve in two cases of an embodiment of the method of the present invention.
Fig. 5 is a schematic diagram of a system frequency response curve with or without energy storage participating in system frequency adjustment according to an embodiment of the method of the present invention.
Detailed Description
A schematic process flow diagram of the method of the present invention is shown in fig. 1: the method for judging the frequency safety and stability of the power system considering the energy storage inertia support provided by the invention comprises the following steps:
s1, acquiring parameters of a power grid system to be analyzed before and after adding an energy storage device;
s2, calculating equivalent inertia time constants of the power grid system to be analyzed before and after the energy storage device is added; the method specifically comprises the following steps:
before new energy is considered to be accessed, the equivalent inertial time constant H of the power grid system to be analyzed is calculated by adopting the following formula T ：
Wherein N is the number of conventional units of the power grid system to be analyzed; h i,sys An equivalent inertial time constant provided for the ith unit for the whole system, and
H i is the inertia time constant of the ith unit, S i Is the capacity of the ith unit, S sys Capacity of a system general assembly machine;
after new energy is considered to be accessed, the equivalent inertial time constant H 'of the power grid system to be analyzed is calculated by adopting the following formula' T ：
H' T ＝H T (1-β)
Wherein beta is the permeability of new energy after being accessed into a power grid system to be analyzed;
s3, calculating an equivalent inertia time constant of the power grid system to be analyzed after energy storage virtual inertia control is performed; the method specifically comprises the following steps:
the equivalent inertia time constant H of the power grid system to be analyzed after the energy storage virtual inertia control is obtained by adopting the following calculation formula W ：
In H' T In order to consider equivalent inertial time constant H 'of power grid system to be analyzed after new energy is accessed' T The method comprises the steps of carrying out a first treatment on the surface of the K is an energy storage virtual inertia control parameter; s is S ESS Is the capacity of the energy storage device; s is S sys Capacity of a system general assembly machine;
s4, calculating to obtain a critical value of an equivalent inertia time constant of the system according to the maximum value of the frequency change rate of the power grid system to be analyzed; the method specifically comprises the following steps:
the critical value H of the equivalent inertial time constant of the system is calculated by adopting the following formula cr ：
In RoCoF max The maximum value of the frequency change rate of the power grid system to be analyzed; p (P) step The load disturbance of the power grid system to be analyzed;
s5, calculating to obtain an inertia support analysis margin of the energy storage system of the power grid system to be analyzed and an equivalent inertia time constant safety margin of the power grid system to be analyzed according to the calculation results of the steps S2-S4;
the inertia support analysis margin eta of the energy storage system of the power grid system to be analyzed on the system is calculated by adopting the following formula:
h in W The method comprises the steps of controlling the energy storage virtual inertia of a power grid system to be analyzed according to an equivalent inertia time constant; h'. T Analyzing an equivalent inertial time constant of the power grid system for considering new energy access; h cr The method comprises the steps of determining a critical value of an equivalent inertial time constant of a power grid system to be analyzed;
the safety margin lambda of the equivalent inertial time constant of the power grid system to be analyzed is obtained by adopting the following formula:
h in W The method comprises the steps of controlling the energy storage virtual inertia of a power grid system to be analyzed according to an equivalent inertia time constant; h cr The method comprises the steps of determining a critical value of an equivalent inertial time constant of a power grid system to be analyzed; h T The equivalent inertia time constant of the power grid system to be analyzed before the energy storage device and the new energy are connected is increased;
s6, carrying out final frequency safety and stability judgment of the power system according to the inertia support analysis margin and the equivalent inertia time constant safety margin which are calculated in the step S5; the method specifically comprises the following steps:
(1) According to the inertia support analysis margin eta, the following rule is adopted for judging:
if eta is more than 0, the transient response process of the power grid system to be analyzed is judged to be safe and stable;
if eta is more than-1 and less than 0, judging that the transient response process of the power grid system to be analyzed is unsafe and stable;
if eta is less than-1, judging the transient response process of the power grid system to be analyzed as safe and stable;
if eta= -1, judging the transient response process of the power grid system to be analyzed as critical safety and stability;
if eta=0, the energy storage has no inertia supporting effect on the system, if H' T -H cr The transient response process of the system is judged to be safe and stable if the transient response process is more than 0; if H' T -H cr < 0, the transient response process of the system is judged to be unsafe and stable;
(2) According to the safety margin lambda of the equivalent inertia time constant, the following rule is adopted for judging:
if lambda is more than 0, the equivalent inertia time constant margin of the power grid system to be analyzed is judged to be safe;
if lambda is less than 0, the equivalent inertia time constant margin of the power grid system to be analyzed is judged to be unsafe.
The deduction process of the method is as follows:
the relation that synchronous machine moment of inertia, active power and system frequency satisfy is:
wherein H represents the time constant of the generator set; Δf is the frequency deviation of the system; p (P) m Is the per unit value of the mechanical power of the prime motor; p (P) e Is the per unit value of electromagnetic power (which can be seen as the system load); d is the generator damping coefficient;
considering that the energy storage system adopts droop control and virtual inertia control to participate in system frequency adjustment, the energy storage droop control power in the system is assumed to be P droop The equivalent inertia time constant of the system is H, and when no virtual inertia control exists, the system meets the following conditions:
after adding the "virtual" inertia, the system satisfies:
increasing the equivalent inertia time constant of the system after virtual inertia control to be H+K/2; when K is more than 0, the equivalent inertia of the system can be increased;
when no new energy is available in the system, the equivalent inertial time constant of the ith unit of the system for the whole system can be calculated by the following formula:
h in i,sys Equivalent inertial time constant(s), H provided for the ith unit for the whole system i Is the inertia time constant of the ith unit, S i The capacity of the ith unit is N is the number of conventional units in the system, S sys Is the capacity of the system assembly machine.
Assuming that the equivalent inertial time constant of the system is H T The total capacity of the system is S sys If a conventional unit is replaced by a new energy unit in the system, the equivalent inertial time constant H of the equivalent system T Will become smaller. When the system units are all conventional units, the equivalent inertia time constant H of the system T Can be expressed as follows:
the relation between the equivalent inertial time constant of the system after the new energy is accessed into the system and the equivalent inertial time constant of the original system is H' T ＝H T (1-beta), wherein beta represents the permeability of the new energy after being accessed into the system;
in the frequency dynamic response process, the rate of change of frequency (Rate of Change of Frequency, rocofis) is an important indicator. When the system rocif is larger, the distributed new energy protection action is caused, and then the distributed new energy is off-grid, so that the system power shortage is further increased, and the safety and stability in the transient response process of the system frequency are not facilitated. The rocofs are taken as constraints to analyze the inertia of the system after the new energy is accessed into the system, and when the disturbance occurs, namely t=0, the maximum value of the frequency change rate is corresponding, namely the rocofs max ：
P in the formula step Is a load disturbance;
in the case of determining the most severe single fault disturbance of the system, according to rocofs max The critical value of the equivalent inertia time constant of the system can be obtained by solving the equation H cr . With the large-scale new energy access, if the new energy cannot provide the system inertia, the system inertia is greatly reduced. Therefore, by configuring energy storage and adopting virtual inertia control, rotational inertia is provided for the system in the transient response process so as to keep the safety and stability of the system frequency.
The relation between the system equivalent inertial time constant after the new energy is accessed into the system and the equivalent inertial time constant of the original system is as follows:
H' T ＝H T (1-β)
on the basis of solving an equivalent inertia time constant of the system and a critical equivalent inertia constant of the system after the new energy is accessed, when the system inertia can not meet the system requirement, the minimum inertia time constant delta H which is required to be provided by the energy storage system to participate in the system frequency response can be obtained simultaneously.
ΔH＝H cr -H’ T
When delta H is more than 0, the equivalent inertia time constant of the system after being connected into new energy is smaller than the critical value, which is unfavorable for the safety and stability of the system frequency. When delta H is less than 0, the equivalent inertia time constant of the system meets the system requirement. According to analysis and solution of the equivalent inertial time constant of the system, the equivalent inertial time constant of the system after the energy storage virtual inertia control is considered can be expressed as H W And needs to satisfy H W ＞H cr 。
And carrying out per unit on the energy storage virtual inertia control output quantity according to the energy storage virtual inertia control link. Because the duration of the transient process is not long, the energy storage can be considered to be supported by the maximum power in the response process, and the charging and discharging time of the energy storage can be taken to be 1 hour, so that the energy storage capacity configuration value is the energy storage power value
S in ESS Configuring a capacity for the stored energy;
when the unit capacity in the system meets S sys ＞＞S ESS In this case, the above formula can be simplified to obtain a formula
At the moment, the equivalent inertial time constant of the system after energy storage access can be calculated through the equation. But when the unit capacity in the system does not satisfy S sys ＞＞S ESS When it is still used
And analyzing the equivalent inertial time constant of the system after the energy storage is accessed.
When the system inertia cannot meet the frequency response requirement due to the fact that the new energy permeability of the system is large, according to the analysis, the system inertia can be increased by configuring energy storage. When the virtual inertia control parameter K of the energy storage system is determined and H W ＝H cr In this case, the minimum value of the energy storage capacity configuration can be obtained from the equation (10). Adding energy storage capacity S ESS And when the energy storage virtual inertia control parameter K is a fixed value, the inertia support requirement can be met by adjusting the energy storage virtual inertia control parameter K.
The new energy permeability of the system is beta, and when the new energy permeability of the system is increased by delta beta, the equivalent inertial time constant variation of the system is delta H RES As the permeability of new energy increases, the inertia of the system must be reduced. If the energy storage configuration capacity delta S can be increased at the moment ESS The system inertia reduced due to the increase of the new energy access proportion is compensated by virtual inertia control in the transient response process, so that the new energy permeability variation and the energy storage capacity variation can be obtainedMathematical relationship of the quantities, as shown in the following formula:
when analysis is performed according to the above formula, the required energy storage configuration capacity change Δs can be calculated by considering that the new energy permeability increases by 1%, i.e., Δβ=0.01 ESS . When Δβ is small, Δs ESS The value is not large, and can be ignored
Middle DeltaS ESS Influence on denominator, so->
In order to quantitatively analyze the supporting effect of a certain capacity energy storage system on the system inertia through virtual inertia, an analysis index eta of the energy storage system on the inertia support is defined, and therefore safety and stability of the system in the frequency transient response process are analyzed.
Wherein H is W To configure the equivalent inertial time constant of the system after the energy storage system, H' T Is equivalent inertial time constant of the system when no energy storage is configured, H cr To consider the system rocofe max Critical inertial time constant of the system in the case.
The eta value characterizes an inertia margin of the energy storage which is increased on the basis of the inertia margin level of the existing system, and therefore the safety and stability of the system frequency in the transient response process are judged. And when eta is more than 0, the system inertia time constant after the new energy is accessed does not reach a critical value, the energy storage further supports the system inertia through virtual inertia control, and the transient response process of the system frequency is safe and stable. And when eta is less than 0, the inertia time constant of the system after the new energy is accessed is lower than a critical value, and the energy storage controls the inertia of the supporting system through the virtual inertia. When-1 < eta < 0The energy storage inertia supporting effect is insufficient to enable the system inertia to be restored to a critical value, and the transient response process of the system frequency is unsafe and unstable; when eta < -1, the energy storage inertia supporting function is expressed, so that the transient response process of the system frequency is safe and stable. When eta= -1, the system inertia reaches a critical value just when the energy storage inertia supporting effect is shown, and the transient response process of the system frequency is critical, safe and stable. When η=0, it indicates that the energy storage has no supporting effect on the inertia of the system after being accessed, and the safety and stability of the transient response process of the system frequency need to be passed
If H 'is the positive or negative judgment of the denominator of (2)' T -H cr The transient response process of the system is judged to be safe and stable if the transient response process is more than 0; if H' T -H cr < 0, the transient response process of the system is judged to be unsafe and stable.
Defining index lambda to represent safety margin level of equivalent inertial time constant of system after new energy and energy storage are accessed and equivalent inertial time constant of original system, as shown in the following formula
When lambda > 0, the equivalent inertia time constant margin of the system is safe, and the larger the value is, the inertia level of the system is approximately close to the state before the new energy is accessed; when λ < 0, the equivalent inertial time constant margin of the system is unsafe.
The method of the invention is further described in connection with one specific example as follows:
taking an IEEE30 node system as an example, the installed capacity of the system is 425MW, the system load is 285MW, the units are conventional units, and the equivalent inertial time constant H of the system is the same at the moment T 6.5s. The 100MW conventional unit at the node 2 is replaced by a new energy unit, the new energy permeability beta is 23.5%, and the equivalent inertial time constant H 'of the system is the same' T 4.97s. The new energy unit is regarded as a constant power source and does not participate in the frequency regulation process of the system.
The energy storage system is added to participate in system frequency adjustment, and the energy storage system only considers virtual inertia control. The frequency response curve of the system with or without energy storage participating in the frequency adjustment is shown in fig. 2. As can be seen from fig. 2, after the energy storage virtual inertia control is added, the inertia of the system can be effectively supported, and the time for the system to reach the lowest frequency point is prolonged.
And when the virtual inertia control parameter K of the energy storage system is 20, the capacity of the energy storage system is 20MWh. Load disturbances were set at t=5s, with a disturbance size of 45MW. The frequency response curves of the systems with or without the energy storage system participating in the frequency adjustment are compared as shown in fig. 3. The rocif=0.529 Hz/s of the system when the stored energy does not participate in the system frequency response. When the energy storage system participates in system frequency adjustment through virtual inertia control, the inertia of the system and the steady-state frequency of the system can be improved, and the safety and stability of the system frequency after disturbance are facilitated. After the energy storage system participates in the frequency response, the rocof0.49 Hz/s of the system (calculated according to the frequency response curve of the system) is calculated according to the formula, the equivalent inertial time constant of the system is 5.399s (H W = 5.441), the support amount of the energy storage system virtual inertia control on the inertia time constant of the whole system is 0.429s, which indicates that the energy storage system plays an inertia support role on the system.
At this time, take the RoCoF max =1.0 Hz/s, then H cr =2.65 s. By computational analysis it is possible to obtain: h'. T ＝4.97s，H W = 5.399s, from which: η=0.185, λ=0.714.
After the frequency response of the energy storage participation system is considered, the equivalent inertia time constant increased by the system is calculated according to a formula, the inertia time constant value increased by the virtual inertia control of the energy storage system is superimposed on the equivalent inertia time constant of the system, and the frequency response curves of the system which are not superimposed and superimposed are compared, as shown in figure 3. As can be seen from the figure, the frequency response of the system is completely consistent in the two cases, and the energy storage virtual inertia control mainly provides inertia support for the system but does not provide power support, so that after the energy storage provides inertia support effect and is superimposed on the equivalent inertia time constant of the system, the inertia support effect of the system is consistent.
When the frequency of the systemRate of change constrained rocofs max When =0.5 Hz/s and no energy storage is configured to participate in system frequency regulation, the system transient frequency response is unsafe and unstable, and the system maximum frequency change rate is greater than rocofs max . According to the constraint condition, the critical inertia time constant H of the system cr =5.29 s, when H W ＝H cr And when the energy storage system participates in the transient response of the system frequency, the equivalent inertial time constant variation of the system is 0.32s. Thus calculated according to the following formula:
From this, S is calculated ESS =13.6 MWh, η= -1; h is calculated according to the frequency response curve W ＝5.294s。
From this, k=18.13, η= -1; h is calculated according to the frequency response curve W ＝5.294s。
Since the above two cases are such that the equivalent inertia constant of the system after adding energy storage is equal to the critical value, λ=0.
The frequency response curves of the system in both cases are shown in fig. 4, and it can be seen from the graph that the frequency response curves of the system in both cases are completely identical. Therefore, under the condition that the required inertia support is certain, the inertia support effect can be changed by changing the virtual inertia control coefficient K of the energy storage system, and the energy storage capacity configuration S can be changed ESS To change the inertial support.
When the energy storage capacity in the system is larger, the equivalent inertia time constant of the system is calculated by the following formula.
Assume a system energy storage configuration capacity S ESS =100 mwh, k=20, rocofs were taken max =1.0 Hz/s, then H cr =2.65 s. The system frequency response curves with or without energy storage participating in the system frequency adjustment are compared as shown in fig. 5.
By computational analysis it is possible to obtain: h'. T =4.02 s, from the above formula H can be found W = 5.924s, solving to obtain H according to the simulation curve W =5.92 s, the resulting errors of the formula calculation and the simulation curve calculation are acceptable. From this calculation: η=1.387, λ=0.85, and the equivalent inertial time constant of the system is still greater than the case that the system is not connected to the energy storage. In this scenario, if the new energy permeability increases by 1%, it can be obtained from the calculation that the system needs to increase the energy storage by about 3.41MWh to maintain the inertia of the system unchanged.
Comprehensive simulation analysis shows that the frequency response of the energy storage participation system is configured in the system, and the virtual inertia control is utilized to increase the inertia of the system, so that the frequency safety and stability of the transient response process of the system are facilitated. For a system with higher new energy permeability, the requirement of large-scale access of new energy can be met by adding energy storage configuration. Under the condition of not considering capacity limitation, the energy storage virtual inertia control and energy storage configuration capacity of a certain new energy permeability system under the condition of meeting the constraint of the frequency change rate (RoCoF) can be analyzed and obtained, and then the aspects of new energy consumption, peak shaving and the like can be further combined, so that the method is favorable for guiding new energy access and energy storage configuration capacity selection, and has very important engineering practical significance in actual power grid operation.
Claims (1)
1. A frequency safety and stability judging method of an electric power system considering energy storage inertia support comprises the following steps:
s1, acquiring parameters of a power grid system to be analyzed before and after adding an energy storage device;
s2, calculating equivalent inertial time constant of the power grid system to be analyzed before new energy is accessed
Equivalent inertial time constant of power grid system to be analyzed after new energy is accessed +.>
；
S3, calculating an equivalent inertia time constant of the power grid system to be analyzed after energy storage virtual inertia control is performed
；
S4, according to the maximum value of the frequency change rate of the power grid system to be analyzed
Calculating to obtain critical value of equivalent inertial time constant of power grid system to be analyzed>
；
S5, calculating to obtain an inertia support analysis margin of the energy storage system of the power grid system to be analyzed on the system according to the calculation results of the steps S2-S4
And equivalent inertial time constant safety margin of the grid system to be analyzed +.>
；
S6, analyzing the margin according to the inertia support calculated in the step S5
And equivalent inertial time constant safety margin +.>
Carrying out final frequency safety and stability judgment of the power system;
step S2, calculating equivalent inertial time constant of the power grid system to be analyzed before new energy is accessed
Equivalent inertial time constant of power grid system to be analyzed after new energy is accessed +.>
The method specifically comprises the following steps:
before new energy is considered to be accessed, the equivalent inertial time constant of the power grid system to be analyzed before the new energy is accessed is calculated by adopting the following formula
：
after the new energy is considered to be accessed, calculating the equivalent inertial time constant of the power grid system to be analyzed after the new energy is accessed by adopting the following formula
：
step S3, calculating an equivalent inertia time constant of the power grid system to be analyzed after energy storage virtual inertia control is performed
The method specifically comprises the following steps:
the equivalent inertia time constant of the power grid system to be analyzed after the energy storage virtual inertia control is obtained by adopting the following calculation formula
：
the maximum value of the frequency change rate according to the power grid system to be analyzed in step S4
Calculating to obtain critical value of equivalent inertial time constant of power grid system to be analyzed>
The method specifically comprises the following steps:
the following formula is adopted to calculate and obtain the critical value of the equivalent inertia time constant of the power grid system to be analyzed
：
In->
The maximum value of the frequency change rate of the power grid system to be analyzed; />
The load disturbance of the power grid system to be analyzed;
s5, analyzing margin of inertia support of the energy storage system of the power grid system to be analyzed on the system
Specifically, the inertia support analysis margin of the energy storage system of the power grid system to be analyzed on the system is calculated by adopting the following formula>
：
step S5 is a safety margin of equivalent inertial time constant of the power grid system to be analyzed
Specifically, the equivalent inertial time constant safety margin of the power grid system to be analyzed is calculated by adopting the following formula>
：
step S6 is performed to obtain the inertia support analysis margin calculated in step S5
And equivalent inertial time constant safety margin +.>
The final frequency safety and stability judgment of the power system is carried out, and the method specifically comprises the following steps:
(1) Based on inertia support analysis margin
The following rules are used for the determination:
if it is
The transient response process of the power grid system to be analyzed is judged to be safe and stable;
if it is
The transient response process of the power grid system to be analyzed is judged to be unsafe and stable;
if it is
The transient response process of the power grid system to be analyzed is judged to be safe and stable;
if it is
Judging the transient response process of the power grid system to be analyzed as critical safety and stability;
if it is
The energy storage has no inertia supporting effect on the system, if ∈>
The transient response process of the system is determined to be safe and stable; if->
The transient response process of the system is judged to be unsafe and stable;
(2) According to the safety margin of the equivalent inertia time constant
The following rules are used for the determination:
if it is
The equivalent inertia time constant margin of the power grid system to be analyzed is judged to be safe; />
If it is
And judging that the equivalent inertia time constant margin of the power grid system to be analyzed is unsafe. />
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