CN110854926B - Method and device for analyzing transient frequency response characteristics of power system after wind power access - Google Patents
Method and device for analyzing transient frequency response characteristics of power system after wind power access Download PDFInfo
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Abstract
The invention discloses a method and a device for analyzing transient frequency response characteristics of a power system after wind power access. The analysis method comprises the following steps: replacing at least one thermal power generating unit in a power system to be analyzed with a wind power generating unit in an equal amount, and determining a wind power access ratio alpha of the power system to be analyzed; determining equivalent inertia time constant T of power system after wind power is connected eq (ii) a Determining a specific regulated power K of an electrical power system S (ii) a Load change delta P of the power system to be analyzed L And then, determining the maximum frequency offset delta f of the power system to be analyzed in the transient process after wind power access when the thermal power generating unit and the load participate in primary frequency modulation together max . The method and the device provide a method for quantitatively analyzing the frequency deviation degree of the power system after the power system is in fault in a large-scale wind power grid-connected state, and are beneficial to improving the wind power access proportion while realizing the safe operation of a power grid.
Description
Technical Field
The invention relates to the technical field of power system engineering, in particular to a method and a device for analyzing transient frequency response characteristics of a power system after wind power is accessed.
Background
In recent years, new energy power generation technology mainly based on wind power in China is rapidly developed. Taking the northeast power grid as an example, in 2019, the northeast wind power total installed capacity exceeds 3100 ten thousand kilowatts, accounts for more than 20% of the total installed capacity of the northeast power grid, and shows a trend of increasing continuously.
After large-scale wind power is connected into an electric power system, due to the unique structure and operation mode of a fan and the restriction of weather conditions, the wind power has the characteristics of randomness and intermittence, so that the capacity of the electric power system for coping with power shortage and power fluctuation is deteriorated after a large number of fans are connected to the grid, and the problem of frequency stability under the actual working condition is frequent. The frequency stabilization influence has global property, and once the stability is damaged, a blackout accident may occur. Therefore, analysis and research on transient frequency characteristics and corresponding optimization control measures of a large-scale wind power grid-connected power system are urgently needed, and more new energy sources such as wind power and the like are received while safe operation of a power grid is guaranteed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method and a device for analyzing the transient frequency response characteristic of a power system after wind power access, and aims to solve the problem of low efficiency of the existing method for analyzing the transient frequency response characteristic of the power system after wind power access.
In a first aspect, the present invention provides a method comprising:
replacing at least one thermal power generating unit in a power system to be analyzed with a wind power generating unit in an equal amount, and determining a wind power access ratio alpha of the power system to be analyzed;
according to the obtained inertia time constant T of the thermal power generating unit before the wind power of the power system to be analyzed is accessed i And the wind power access ratio alpha is used for determining the equivalent inertia time constant T of the power system after the wind power access eq ；
According to the acquired unit regulation power K of the thermal power generating unit before wind power access of the electric power system to be analyzed G Specific regulated power K of the load of the power system to be analyzed L And the wind power access ratio alpha, determining the unit regulation power K of the power system S ；
Load change delta P of the power system to be analyzed L And then, determining the maximum frequency offset delta f of the power system to be analyzed in the transient process after wind power access when the thermal power generating unit and the load participate in primary frequency modulation together max 。
Further, still include:
the maximum frequency offset Δ f to be determined max Comparing with a preset offset threshold;
at the maximum frequency offset Δ f max When the deviation is larger than the preset deviation threshold value, the wind power access ratio alpha is kept unchanged,
in the aspect of wind generation sets, adding a virtual inertia control link or an active-frequency droop control link to enable the maximum frequency offset delta f max Decreasing to no greater than the predetermined offset threshold;
on the aspect of the thermal power generating unit, the rotation reserve capacity of the thermal power generating unit or the number of the thermal power generating units is increased, or the difference adjustment coefficient of a speed regulator of a steam turbine is changed or the frequency modulation dead zone is reduced, so that the maximum frequency offset delta f max To not greater than the predetermined offset threshold.
In a second aspect, the present invention provides an apparatus for analyzing transient frequency response characteristics of a power system after wind power access, including:
the system comprises a wind power access ratio determining module, a power analysis module and a power analysis module, wherein the wind power access ratio determining module is used for replacing at least one thermal power generating unit in a power system to be analyzed with a wind power generating unit in an equal amount and determining a wind power access ratio alpha of the power system to be analyzed;
the equivalent inertia time constant determination module is used for determining the inertia time constant T of the thermal power generating unit before the wind power is accessed according to the acquired inertia time constant T of the power system to be analyzed i And the wind power access ratio alpha is used for determining the equivalent inertia time constant T of the power system after the wind power access eq ；
The unit regulation power determining module of the power system is used for determining the unit regulation power K of the thermal power generating unit before wind power access of the power system to be analyzed according to the acquired unit regulation power K of the thermal power generating unit before the wind power access of the power system to be analyzed G Specific regulated power K of the load of the power system to be analyzed L And the wind power access ratio alpha, determining the unit regulation power K of the power system S ；
A maximum frequency offset determination module for determining the load change Δ P of the power system to be analyzed L And then, determining the maximum frequency offset delta f of the power system to be analyzed in the transient process after wind power access when the thermal power generating unit and the load participate in primary frequency modulation together max 。
The method and the device for analyzing the transient frequency response characteristics of the power system after wind power access firstly construct a calculation formula of the inertia time constant and the power regulation capability of the system under different wind power access ratios; and a calculation formula of the maximum frequency deviation under the fault condition is constructed and used for evaluating the transient frequency deviation degree of the system. The analysis method and the device provide a method for quantitatively analyzing the frequency deviation degree of the power system after the power system fails in a large-scale wind power grid-connected form, and are beneficial to improving the wind power access proportion while realizing the safe operation of a power grid.
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Exemplary embodiments of the invention may be more completely understood in consideration of the following drawings:
FIG. 1 is a schematic flow diagram of a process according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of the composition of the apparatus of the preferred embodiment of the present invention.
Fig. 3 is a flowchart of analyzing and optimizing transient frequency response characteristics of a power system after wind power is connected in the preferred embodiment of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
With the increasing year by year of installed capacity of new energy sources such as wind power and the like, a large number of power electronic devices replace traditional electromagnetic conversion devices of a power system. Due to the unique structure and the operation mode of the fan, the fan does not have the frequency response capability of a synchronous generator, and the capability of a power system for coping with power shortage and power fluctuation is deteriorated after a large number of fans are connected to the grid.
The influence on the frequency of the power system after wind power access mainly comprises the following steps: (1) the output fluctuation of wind power per se causes disturbance of the system frequency, and the fluctuation puts higher requirements on the frequency modulation abundance, the frequency modulation flexibility and the climbing capability of the system; (2) the main stream variable speed wind turbine generator set can not respond to the change of the system frequency like a synchronous generator because the rotating speed and the frequency are completely decoupled. After the variable-speed wind turbine generator replaces a synchronous generator in a large scale, the equivalent inertia time constant of the system is reduced, and the active power dynamic control capability of the power system is reduced; (3) the fault ride-through capability of wind power is limited, and the wind power is easy to be off-line, so that the frequency stability of the system is further deteriorated. In addition to the characteristics of randomness and volatility of wind power, the problem of frequency stability under actual working conditions is more frequent, especially under extreme working conditions, safety control protection actions such as low-frequency load shedding, high-frequency generator tripping and the like can be triggered when the change rate and the degree of the frequency are too large, the difficulty of operation, protection and scheduling of a power grid in a high-permeability area of the wind power is further increased, new challenges are brought to the safety and stability of the frequency of the power grid, and the wind power consumption is restricted to a certain extent.
In order to improve the wind power consumption level, early measures were to alleviate the active power balance of the system by increasing a certain spare capacity. With the continuous rising of the wind power grid-connected capacity, the required reserve capacity is also continuously improved, which is not beneficial to the economic operation of the power grid, and meanwhile, the load of the power grid dispatching is also increased.
In order to ensure safe and economic operation of a power grid, some countries such as Denmark, Ireland and the like put forward the requirement that wind power participates in frequency modulation. The national technical standard of wind power participating in frequency modulation provided by China indicates that the wind power of China has the capacity of participating in frequency modulation and peak shaving of a power system. At present, the frequency of a system is improved by the wind turbine generator participating in auxiliary frequency modulation, so that a power grid can accept new wind power energy in a larger proportion.
It should be understood that the power system includes: a wind power generation unit or a thermal power generation unit as a power supply, a load, and a line connecting the power supply and the load. The thermal power generating unit is usually a turbine generator, and the turbine generator is provided with a synchronous generator and a speed regulator. The wind turbines are typically doubly-fed variable speed wind turbines (including wind generators). The main line of the power system is a three-phase line, and has a single circuit and a double circuit; a single-phase fault or a multi-phase fault (here, a multi-phase fault, which is a two-phase fault or a three-phase fault) may occur in a three-phase line.
As shown in fig. 1, the method for analyzing transient frequency response characteristics of a power system after wind power access according to an embodiment of the present invention includes:
step S10: replacing at least one thermal power generating unit in a power system to be analyzed with a wind power generating unit in an equal amount, and determining a wind power access ratio alpha of the power system to be analyzed;
step S20: according to the obtained inertia time constant T of the thermal power generating unit before wind power access of the power system to be analyzed i And the wind power access ratio alpha is used for determining the equivalent inertia time constant T of the power system after the wind power access eq ；
Step S30: according to the acquired unit regulation power K of the thermal power generating unit before wind power access of the electric power system to be analyzed G Specific regulated power K of the load of the power system to be analyzed L And the wind power access ratio alpha, determining the unit regulation power K of the power system S ；
Step S40: load change delta P of the power system to be analyzed L And then, determining the maximum frequency offset delta f of the power system to be analyzed in the transient process after wind power access when the thermal power generating unit and the load participate in primary frequency modulation together max 。
The method provides a quantitative calculation method of the inertia time constant of the system and the power regulation capacity of the system after wind power is connected, and a quantitative calculation method of the maximum frequency deviation of the system after disturbance, and is the basis for quantitative analysis and evaluation of the frequency deviation characteristics of the system after wind power integration.
Further, the method also comprises the following steps:
the maximum frequency offset Δ f to be determined max Comparing with a preset offset threshold;
at the maximum frequency offset amount deltaf max When the deviation value is larger than the preset deviation threshold value, the wind power access ratio alpha is kept unchanged,
in the aspect of wind turbine generators, a virtual inertia control link or an active-frequency droop control link is added, so that the maximum frequency offset delta f max Decreasing to no greater than the predetermined offset threshold;
on the aspect of the thermal power generating unit, the rotation reserve capacity of the thermal power generating unit or the number of the thermal power generating units is increased, or the difference adjustment coefficient of a speed regulator of a steam turbine is changed or the frequency modulation dead zone is reduced, so that the maximum frequency offset delta f max To not greater than the predetermined offset threshold.
If the maximum frequency deviation is larger than the preset maximum frequency deviation allowable threshold value under the current access proportion and in the case of a certain predicted fault, corresponding frequency optimization control measures are taken to reduce the maximum frequency deviation, so that the frequency characteristic of the system is improved.
The method also provides corresponding frequency optimization measures, and is beneficial to improving the proportion of wind power access while realizing the safe operation of the power grid.
Further, at least one thermal power generating unit in the power system to be analyzed is replaced by a wind power generating unit, and a wind power access ratio alpha of the power system to be analyzed is determined, including:
the method comprises the steps of obtaining the total rated capacity of a thermal power generating unit of a power system to be analyzed before wind power is accessed and the total rated capacity of the thermal power generating unit after the wind power is accessed, and determining the wind power access ratio alpha of the power system to be analyzed according to the following formula:
before the wind power of the power system to be analyzed is accessed, n thermal power generating units are arranged; when wind power is connected, k thermal power generating units are replaced by wind power generating units in equal amount; p Gi The rated active power of the synchronous generator in the ith thermal power generating unit.
Further, according to the obtained inertia time constant T of the thermal power generating unit before wind power access of the power system to be analyzed i And the wind power access ratio alpha is used for determining the equivalent inertia time constant T of the power system after the wind power access eq The method comprises the following steps:
when the inertia time constants of the thermal power generating units are approximately equal, acquiring the inertia time constant T of the thermal power generating unit before wind power access of the power system to be analyzed i And the wind power access ratio alpha, and determining the equivalent inertia time constant T of the power system after the wind power access according to the following formula eq ：
Wherein, T i The inertia time constant of the ith thermal power generating unit is obtained;
J si 、P si 、ω si respectively the rotational inertia, the polar pair number and the synchronous angular speed of the ith thermal power generating unit;
and T is an inertia time constant of the thermal power generating unit of the power system to be analyzed before wind power is accessed.
Further, the power K is adjusted according to the obtained unit of the thermal power generating unit of the electric power system to be analyzed before wind power access Gi Specific regulated power K of the load of the power system to be analyzed L And the wind power access ratio, determining the unit regulating power K of the power system S The method comprises the following steps:
when each thermal power generating unit has primary frequency modulation capability and the unit regulating power of each thermal power generating unit is approximately equal, the unit regulating power K of the thermal power generating unit before wind power access of the electric power system to be analyzed is obtained Gi And the wind power access ratio alpha, and determining the equivalent unit regulation power K of the thermal power generating unit after the wind power access according to the following formula Geq ：
K Gi adjusting power for the unit of the ith thermal power generating unit;
K G adjusting power for the unit of all n thermal power generating units in the system before wind power is accessed;
K Geq adjusting power for equivalent units of all (n-k) thermal power generating units in the system after wind power is accessed;
the specific regulating power K of the load after and before the wind power access L When the power is not changed, determining the unit regulating power K of the power system to be analyzed according to the following formula S ：
K S ＝K Geq +K L 。
Further, the load change Δ P of the power system to be analyzed L And then, determining the maximum frequency offset delta f of the power system to be analyzed in the transient process after wind power access when the thermal power generating unit and the load participate in primary frequency modulation together max The method comprises the following steps:
upon detection of a load change Δ P of the power system to be analyzed L And after detecting the frequency deviation of the electric power system to be analyzed, putting the thermal power generating unit and the load into participation in primary frequency modulation at the same time, and determining the maximum frequency deviation delta f of the electric power system to be analyzed in the transient process according to the following formula max ：
Furthermore, the power system to be analyzed comprises t trunk lines;
the fault corresponding to each trunk line is any one of the following faults: the main protection refuses to be performed by single-phase permanent short-circuit fault, three-phase permanent short-circuit fault, double-circuit line different-name phase-to-phase short-circuit fault and double-circuit line different-name phase-to-phase short-circuit fault;
wherein the corresponding fault of the main line causes the load change delta P of the power system to be analyzed L And causing the power system under analysis to enter a transient process.
Further, in the power system to be analyzed, the wind power generation unit or the thermal power generation unit is a power supply;
the thermal power generating unit is a turbine generator provided with a speed regulator and a synchronous generator;
the wind turbine generator is a double-fed variable speed wind turbine generator.
The method provides a simple and feasible method for quantitative evaluation of the frequency deviation characteristic of the power system after wind power is accessed, forms an evaluation flow and an optimization control flow of the transient frequency deviation characteristic under the disturbance condition, and enables a power grid to furthest consume new wind power energy under the condition of ensuring safe and stable operation of the system.
As shown in fig. 2, the transient frequency response characteristic analysis apparatus of the power system after wind power access according to the embodiment of the present invention includes:
the wind power access ratio determining module 100 is configured to replace at least one thermal power generating unit in the power system to be analyzed with a wind power generating unit, and determine a wind power access ratio α of the power system to be analyzed;
an equivalent inertia time constant determination module 200, configured to determine an inertia time constant T of the thermal power generating unit before wind power is accessed according to the acquired inertia time constant T of the power system to be analyzed i And the wind power access ratio alpha is used for determining the equivalent inertia time constant T of the power system after the wind power access eq ；
A unit regulation power determining module 300 of the power system, configured to obtain a unit regulation power K of the thermal power generating unit before wind power access of the power system to be analyzed G Specific regulated power K of the load of the power system to be analyzed L And the wind power access ratio alpha, determining the unit regulation power K of the power system S ；
A maximum frequency offset determination module 400 for determining a load change Δ P of the power system to be analyzed L And then, determining the maximum frequency offset delta f of the power system to be analyzed in the transient process after wind power access when the thermal power generating unit and the load participate in primary frequency modulation together max 。
Further, still include:
a maximum frequency offset adjustment module for comparing the maximum frequency offset Δ f to be determined max Comparing with a preset offset threshold;
at the maximum frequency offset amount deltaf max When the deviation is larger than the preset deviation threshold value, the wind power access ratio alpha is kept unchanged,
in the aspect of wind turbine generators, a virtual inertia control link or an active-frequency droop control link is added, so that the maximum frequency offset delta f max Decreasing to no greater than the predetermined offset threshold;
on the aspect of the thermal power generating unit, the rotation reserve capacity of the thermal power generating unit or the number of the thermal power generating units is increased, or the difference adjustment coefficient of a speed regulator of a steam turbine is changed or the frequency modulation dead zone is reduced, so that the maximum frequency offset delta f max To not greater than the predetermined offset threshold.
The device has the same technical scheme and inventive concept as the method, has the same technical effect, and is not repeated herein.
Fig. 3 shows a specific flow of a method for analyzing and optimizing the transient frequency response characteristics of the power system after wind power access in batch, which is described in detail below.
Step (1): setting a plurality of different wind power access ratios
A plurality of (e.g. k) thermal power generating units in the power system are replaced by double-fed variable speed wind generating units with the same capacity. That is, the total rated capacity (here, the rated active power) of the thermal power generating units is the designated capacity P; the total rated capacity of a plurality of (for example, m) doubly-fed variable speed wind power generation units for replacing the thermal power generation unit is also the designated capacity P.
The method comprises the following steps that n thermal power generating units are assumed in a power system; equally replacing k thermal power generating units in the n thermal power generating units with s wind power generating units, wherein k is less than n; because of equal-amount replacement, the total rated active power generated by the power system is kept unchanged before and after the wind power is connected.
At this time, the wind power access ratio α is:
wherein, alpha is wind power access ratio, P Gi The rated active power of the synchronous generator in each thermal power generating unit.
Changing the total rated capacity of the replaced thermal power generating unit for multiple times; a plurality of different wind power access ratios alpha can be respectively calculated through the formula (1); according to the rated capacity of the k replaced thermal power generating units m times, a wind power access ratio vector alpha comprising m elements can be formed as { alpha ═ alpha 1 ,α 2 …α m }。
Step (2): quantitatively calculating inertia time constant and power regulation capacity under different wind power access ratios
2.1) calculating the time constant T of inertia
Time constant of inertia T i Is defined as: the ratio of the rotor rotation energy storage of the synchronous generator in a single thermal power generating unit at the synchronous angular speed to the rated capacity of the thermal power generating unit. And the equivalent inertia time constant T of the power system can be expressed as the ratio of the total rotor rotation energy storage to the total rated capacity of the power system, namely
In the formula, T i The inertia time constant of the ith thermal power generating unit is obtained, and T is the equivalent inertia time constant of the power system;
J si 、P si 、ω si the rotational inertia, the number of pole pairs and the rotating speed (namely the synchronous angular speed) of the ith thermal power generating unit are respectively;
W Gi the kinetic energy of the rotor (namely the rotor rotation energy storage) of the thermal power generating unit i at the rated rotating speed (namely the synchronous angular speed) is obtained.
From the formula (2), it can be seen that after the wind turbine generator unit replaces the thermal power generator unit and is added into the power system, the numerical value of the rotational energy storage of the whole rotor of the power system is reduced.
If the installed capacities of the thermal power generating units are approximately equal, the definition of the inertia time constant according to the formula (2) can be used for obtaining that the inertia time constant of each thermal power generating unit is approximately equal, and at this time, the following formula (2) is continuously known:
in the formula, T eq And the equivalent inertia time constant of the system after the wind power is connected.
As can be seen from the formula (3), different wind power access ratios correspond to different equivalent inertia time constants.
According to m different wind power access ratios, an equivalent inertia time constant vector T comprising m elements can be formed eq ：T eq ＝{T α1 ,T α2 …T αm }。
2.2) calculation of Power Regulation capability
According to the static characteristic of the synchronous generator, the wind power generation set does not participate in frequency modulation, the wind power generation set replaces a thermal power generation set with primary frequency modulation capability, and before and after wind power is connected, unit regulation power of a power supply in the power system is respectively as follows:
k in the formula (4) Gi For regulating the power, K, of the ith thermal power unit G The power is adjusted for the unit of all n thermal power generating units in the system before wind power is accessed; k is Geq And adjusting power for equivalent units of all (n-k) thermal power generating units in the system after wind power is accessed.
When the unit regulating power of each thermal power generating unit is approximately equal, then
Further, before and after the wind power replacement, the unit regulation power K of the load L If no change occurs, the unit regulated power of the power system is as shown in formula (6)
K S ＝K Geq +K L (6)
In the formula (6), K S For unit regulation of the system, K L The power is adjusted for the unit of load.
The unit adjusting power of the corresponding system under different wind power access ratios can be obtained by the formula (6). According to m different wind power access ratios, a unit regulation power vector K of a system comprising m elements can be formed S ＝{K Sα1 ,K Sα2 …K Sαm }。
The unit regulation power vector of the system can reflect the influence of different wind power access ratios on the power regulation capacity of the system. The larger the wind power access ratio is, the smaller the unit adjusting power of the system is.
And (3): establishment of fault set
Counting all t trunk lines in the power system to form a line set L ═ L 1 ,l 2 …l t H, wherein l t Representing the t-th trunk line of the line. Traversing each trunk line in the line set L for typical faults such as single-phase permanent short-circuit fault, three-phase permanent short-circuit fault, double-circuit line different-name-phase inter-phase short-circuit fault main protection refusal and the like to form a fault set S ═ S 1 ,s 2 …s t }; wherein S is 1 Representing a fault set when different faults occur on the line 1; s t Representing a set of faults when different faults occur on the line t.
And (4): calculation of maximum frequency deviation value of system after fault occurrence
At maximum frequency deviation deltaf max As an index reflecting the primary frequency modulation capability of the system.
Let us assume at t 0 At the moment, the system suffers from a large disturbance, e.g. a sudden increase Δ P in the load on a trunk line L This then results in a reduction in the frequency of the system. After the frequency deviation is detected, the thermal power generating unit and the load jointly participate in primary frequency modulation, and the active power balance equation of the system is as follows in the transient process
In the formula, T eq Is the inertia time constant, K, of a conventional generator set in the system L Regulating power per unit of load in the system, Δ f being the frequency deviation of the system, Δ P G (t) at large disturbances (sudden load addition Δ P) L ) The mechanical power increased by a single thermal power generating unit under the condition; since the wind turbine is assumed not to participate in frequency modulation, delta P W Wind power onlyThe power change of the wind turbine generator caused by fluctuation can approximately consider that the wind power does not fluctuate in a short time period of a large disturbance scene, so that the delta P W Can be ignored, i.e. Δ P W Is zero.
It should be understood that the thermal power generating unit has mechanical power and electromagnetic power, and the mechanical power is referred to in formula (7).
When the load participates in primary frequency modulation, the unit adjusting power K of the load can be approximately considered L No change occurred.
In the process of primary frequency modulation, the thermal power generating unit responds to the frequency deviation of the system through a speed regulator, and the increment delta P of the power G Proportional to the deviation amount of frequency deltaf. The steam turbine model of the thermal power generating unit can be simplified into a first-order inertia link,
in the formula (8), T S Is the governor time constant of the steam turbine; in specific implementation, the time constants of the speed regulators of the steam turbines in the thermal power generating units in the power system can be approximately considered to be equal;
K Geq and adjusting power for equivalent units of all thermal power generating units in the power system.
Substituting the formula (8) into the formula (7) can obtain a differential equation shown as the formula (9)
T eq T S f”+(T eq +T S K L )f'+(K G +K L )f＝K G +K L -ΔP L (9)
In the formula (9), f "is the second reciprocal of the system frequency, f' is the first reciprocal of the system frequency, and when t is t 0 When there is f ═ 1, f ═ Δ P L /T eq 。
This initial condition is brought into the formula (9),
in the formula,
in addition, at the maximum frequency deviation, the frequency change rate is 0, so that the maximum frequency deviation Δ f can be obtained by calculating the first derivative of equation (10) max And the time t at which the frequency drops to the lowest point a As shown in the formula (16),
due to K L ＜＜K Geq γ ≈ sin (γ) ≈ tan (γ), the relevant variables in formula (16) and formula (13) are simplified to obtain,
as can be seen from the relevant properties of the exponential function,
the maximum frequency deviation Δ f max Can be simplified into:
from the equation (18), it is possible to obtain a disturbance amount Δ P L In the case of (2), the wind power cut-in ratio alpha and the maximum frequency deviation delta f max The relationship (2) of (c).
When the wind power access ratio and the disturbance quantity change, the maximum frequency deviation of the system changes correspondingly.
And (5): establishment of maximum frequency deviation matrix delta F
As can be known from the step (2) and the step (4), under the same fault condition, different wind power access ratios affect the inertia time constant of the system and the power regulation capability of the system, so that the maximum frequency deviation of the system is affected.
Under the same wind power access ratio, different faults correspond to different maximum frequency deviations. Thus, a frequency deviation matrix Δ F can be established, as shown in equation (19):
wherein the rows in the matrix represent different wind power access ratios { alpha } 1 ,α 2 …α m } T The columns in the matrix correspond to the fault set types S ═ S of different trunk lines 1 ,s 2 …s t And each element in the matrix represents a maximum frequency deviation value corresponding to a certain fault disturbance under a certain wind power access ratio.
Typically, line faults can cause the load to change; at this time, the load change amount Δ P L May be positive, indicating an increase; load variation amount Δ P L And possibly negative, indicating a decrease.
And (6): establishment of matrix delta F' requiring frequency optimization control
The maximum frequency deviation matrix can be obtained from equation (19). For a power system, the value of the maximum frequency deviation allowed is determinedThus, a threshold value Δ f of the maximum frequency deviation is set set (ii) a Comparing the elements in the delta F with the threshold value, and if a certain element delta F in the maximum frequency deviation number matrix ij Exceeds the threshold value deltaf set If the wind power access ratio is alpha, the wind power access ratio is explained to be alpha i And a failure S occurs j The safety control protection action of low-frequency load shedding or high-frequency cutting machine of the system can be triggered, so that the system has serious operation problems.
Sorting the delta F, comparing the sorted delta F with a threshold value, deleting elements lower than the threshold value, and finally forming a matrix delta F' needing frequency optimization control, wherein any element in the matrix exceeds the set threshold value.
Wherein p is less than or equal to m, and k is less than or equal to n.
That is, less than the threshold value is considered normal operation. For example, if the allowable frequency deviation is 0.5, all frequencies less than 0.5 are considered to be stable.
And (7): frequency optimization related measure making
And (4) formulating corresponding measures for frequency optimization control according to the elements of the matrix delta F' obtained in the step (6) to enable the numerical values in the matrix to be smaller than the set threshold value of the maximum frequency deviation.
After wind power is connected into a power system, frequency optimization control measures need to be formulated from two aspects of a wind power generating unit and a thermal power generating unit. In the aspect of a wind turbine generator, the active output power of a fan can respond to the frequency change of a system by adding an active control link, and the added control mainly comprises the following steps: 1. virtual inertia control is added, the rotational kinetic energy of the fan is coupled with the system frequency, and the dynamic response characteristic of a conventional turbine generator is simulated; 2. an active-frequency droop control link is added to simulate a speed regulator of a turbonator, so that the fan actively participates in primary frequency modulation.
In the aspect of thermal power generating units, measures such as increasing the rotation reserve capacity of the thermal power generating units, increasing the number of the thermal power generating units participating in primary frequency modulation, changing the difference adjustment coefficient of a speed regulator of a steam turbine (which is the reciprocal of unit adjustment power of the thermal power generating units), reducing the range of a frequency modulation dead zone and the like can be adopted to carry out frequency optimization control.
The method for analyzing and optimizing the transient frequency response characteristics of the power system after wind power access combines the relevant characteristics of the system frequency response after wind power access, and constructs the calculation formulas of the inertia time constant and the power regulation capacity of the system under different wind power access ratios; a calculation formula of the maximum frequency deviation of the transient frequency deviation degree of the system under a certain fault condition is provided, and maximum frequency deviation matrixes under different wind power proportions and different fault conditions are obtained; sequencing elements in the matrix and comparing the sequenced elements with a set threshold value of allowed maximum frequency deviation to form a matrix needing frequency optimization control; and (4) according to the elements in the matrix, proposing an optimal control measure of the frequency to reduce the maximum frequency deviation and improve the frequency characteristic of the system. Finally, an evaluation and optimization control flow of the transient frequency deviation characteristic under the disturbance condition is formed, the frequency performance improvement after the wind power and other new energy resources are accessed into the system can be guided, the normal operation of the system after the wind power is accessed in a large scale is ensured, and the power grid can accept the wind power and other new energy resources with higher proportion.
The invention has been described above by reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a// the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of a device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
Claims (7)
1. A method for analyzing transient frequency response characteristics of a power system after wind power access is characterized by comprising the following steps:
replacing at least one thermal power generating unit in a power system to be analyzed with a wind power generating unit in an equal amount, and determining a wind power access ratio alpha of the power system to be analyzed;
according to the obtained inertia time constant T of the thermal power generating unit before the wind power of the power system to be analyzed is accessed i And the wind power access ratio alpha is used for determining the equivalent inertia time constant T of the power system after the wind power access eq The method comprises the following steps: when the inertia time constants of the thermal power generating units are approximately equal, acquiring the inertia time constant T of the thermal power generating unit before wind power access of the power system to be analyzed i And the wind power access ratio alpha, and determining the equivalent inertia time constant T of the power system after the wind power access according to the following formula eq ：
Wherein, T i The inertia time constant of the ith thermal power generating unit is obtained;
J si 、P si 、ω si respectively representing the rotational inertia, the pole pair number and the synchronous angular speed of the ith thermal power generating unit;
t is an inertia time constant of the thermal power generating unit before wind power is accessed to the power system to be analyzed;
according to the acquired unit regulation power K of the thermal power generating unit before wind power access of the electric power system to be analyzed G Specific regulated power K of the load of the power system to be analyzed L And the wind power access ratio alpha, determining the unit regulation power K of the power system S The method comprises the following steps: when each thermal power generating unit has primary frequency modulation capability and the unit regulating power of each thermal power generating unit is approximately equal, the unit regulating power K of the thermal power generating unit before wind power access of the electric power system to be analyzed is obtained Gi And the wind power access ratio alpha, and determining the equivalent unit regulation power K of the thermal power generating unit after the wind power access according to the following formula Geq ：
K Gi adjusting power for the unit of the ith thermal power generating unit;
K G the power is adjusted for the unit of all n thermal power generating units in the system before wind power is accessed;
K Geq adjusting power for equivalent units of all (n-k) thermal power generating units in the system after wind power is accessed;
the specific regulating power K of the load after and before the wind power access L When the power is not changed, determining the unit regulating power K of the power system to be analyzed according to the following formula S ：
K S ＝K Geq +K L ；
Load change delta P of the power system to be analyzed L And then, determining the maximum frequency offset delta f of the power system to be analyzed in the transient process after wind power access when the thermal power generating unit and the load participate in primary frequency modulation together max The method comprises the following steps: upon detection of a load change Δ P of the power system to be analyzed L And after detecting the frequency deviation of the electric power system to be analyzed, putting the thermal power generating unit and the load into participation in primary frequency modulation at the same time, and determining the maximum frequency deviation delta f of the electric power system to be analyzed in the transient process according to the following formula max ：
2. The method for analyzing the transient frequency response characteristic of the power system after wind power access according to claim 1, further comprising:
the maximum frequency offset Δ f to be determined max Comparing with a preset offset threshold;
at the maximum frequency offset Δ f max When the deviation is larger than the preset deviation threshold value, the wind power access ratio alpha is kept notIn the process of changing the shape of the pipe,
in the aspect of wind turbine generators, a virtual inertia control link or an active-frequency droop control link is added, so that the maximum frequency offset delta f max Decreasing to no greater than the predetermined offset threshold;
on the aspect of the thermal power generating unit, the rotation reserve capacity of the thermal power generating unit or the number of the thermal power generating units is increased, or the difference adjustment coefficient of a speed regulator of a steam turbine is changed or the frequency modulation dead zone is reduced, so that the maximum frequency offset delta f max To not greater than the predetermined offset threshold.
3. The method for analyzing transient frequency response characteristics of a wind power system after wind power access according to claim 1,
at least one thermal power generating unit in the electric power system to be analyzed is replaced by a wind power generating unit in an equal amount, and the wind power access ratio alpha of the electric power system to be analyzed is determined, wherein the method comprises the following steps:
the method comprises the steps of obtaining the total rated capacity of a thermal power generating unit of a power system to be analyzed before wind power is accessed and the total rated capacity of the thermal power generating unit after the wind power is accessed, and determining the wind power access ratio alpha of the power system to be analyzed according to the following formula:
before the wind power of the power system to be analyzed is accessed, n thermal power generating units are arranged; when wind power is connected, k thermal power generating units are replaced by wind power generating units in equal amount; p Gi The rated active power of the synchronous generator in the ith thermal power generating unit.
4. The method for analyzing transient frequency response characteristics of a wind power system after wind power access according to claim 3,
the power system to be analyzed comprises t trunk lines;
the fault corresponding to each trunk line is any one of the following faults: the main protection refuses to be performed by single-phase permanent short-circuit fault, three-phase permanent short-circuit fault, double-circuit line different-name phase-to-phase short-circuit fault and double-circuit line different-name phase-to-phase short-circuit fault;
wherein the corresponding fault of the main line causes the load change delta P of the power system to be analyzed L And causing the power system under analysis to enter a transient process.
5. The method for analyzing transient frequency response characteristics of a power system after wind power integration according to claim 3,
in the power system to be analyzed, the wind power generating unit or the thermal power generating unit is a power supply;
the thermal power generating unit is a turbine generator provided with a speed regulator and a synchronous generator;
the wind turbine generator is a double-fed variable speed wind turbine generator.
6. The utility model provides a wind-powered electricity generation access back electric power system transient state frequency response characteristic analysis device which characterized in that includes:
the system comprises a wind power access ratio determining module, a wind power access ratio determining module and a power analysis module, wherein the wind power access ratio determining module is used for replacing at least one thermal power generating unit in a power system to be analyzed with a wind power generating unit in an equal amount and determining a wind power access ratio alpha of the power system to be analyzed;
the equivalent inertia time constant determination module is used for determining the inertia time constant T of the thermal power generating unit before the wind power is accessed according to the acquired inertia time constant T of the power system to be analyzed i And the wind power access ratio alpha is used for determining the equivalent inertia time constant T of the power system after the wind power access eq The method comprises the following steps: when the inertia time constants of the thermal power generating units are approximately equal, acquiring the inertia time constant T of the thermal power generating unit before wind power access of the power system to be analyzed i And the wind power access ratio alpha, and determining the equivalent inertia time constant T of the power system after the wind power access according to the following formula eq ：
Wherein, T i The inertia time constant of the ith thermal power generating unit is obtained;
J si 、P si 、ω si respectively representing the rotational inertia, the pole pair number and the synchronous angular speed of the ith thermal power generating unit;
t is an inertia time constant of the thermal power generating unit before wind power is accessed to the power system to be analyzed;
the unit adjusting power determining module of the power system is used for determining the unit adjusting power K of the thermal power generating unit before the wind power is accessed to the power system to be analyzed according to the obtained unit adjusting power K of the thermal power generating unit before the wind power is accessed to the power system to be analyzed G Specific regulated power K of the load of the power system to be analyzed L And the wind power access ratio alpha is used for determining the unit regulation power K of the power system S The method comprises the following steps: when each thermal power generating unit has primary frequency modulation capability and the unit regulating power of each thermal power generating unit is approximately equal, the unit regulating power K of the thermal power generating unit before wind power access of the electric power system to be analyzed is obtained Gi And determining the equivalent unit regulation power K of the thermal power generating unit after the wind power is accessed according to the following formula Geq ：
K Gi adjusting power for the unit of the ith thermal power generating unit;
K G adjusting power for the unit of all n thermal power generating units in the system before wind power is accessed;
K Geq adjusting power for equivalent units of all (n-k) thermal power generating units in the system after wind power is accessed;
the specific regulating power K of the load after and before the wind power access L When the power is not changed, determining the unit regulating power K of the power system to be analyzed according to the following formula S ：
K S ＝K Geq +K L ；
A maximum frequency offset determination module for determining the load change delta P of the power system to be analyzed L When it is determinedWhen the thermal power generating unit and the load participate in primary frequency modulation together, the maximum frequency offset delta f of the power system to be analyzed in the transient process after wind power access max The method comprises the following steps: upon detection of a load change Δ P of the power system to be analyzed L And after detecting the frequency deviation of the electric power system to be analyzed, putting the thermal power generating unit and the load into participation in primary frequency modulation at the same time, and determining the maximum frequency deviation delta f of the electric power system to be analyzed in the transient process according to the following formula max ：
7. The device for analyzing transient frequency response characteristics of the wind power system after wind power access according to claim 6, further comprising:
a maximum frequency offset adjustment module for comparing the maximum frequency offset Δ f to be determined max Comparing with a preset offset threshold;
at the maximum frequency offset amount deltaf max When the deviation is larger than the preset deviation threshold value, the wind power access ratio alpha is kept unchanged,
in the aspect of wind turbine generators, a virtual inertia control link or an active-frequency droop control link is added, so that the maximum frequency offset delta f max Decreasing to no greater than the predetermined offset threshold;
on the aspect of the thermal power generating unit, the rotation reserve capacity of the thermal power generating unit or the number of the thermal power generating units is increased, or the difference adjustment coefficient of a speed regulator of a steam turbine is changed or the frequency modulation dead zone is reduced, so that the maximum frequency offset delta f max To not greater than the predetermined offset threshold.
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