CN117638990A - Calculation method for decoupling frequency modulation parameter adjustable range of new energy power system - Google Patents

Calculation method for decoupling frequency modulation parameter adjustable range of new energy power system Download PDF

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CN117638990A
CN117638990A CN202311654824.6A CN202311654824A CN117638990A CN 117638990 A CN117638990 A CN 117638990A CN 202311654824 A CN202311654824 A CN 202311654824A CN 117638990 A CN117638990 A CN 117638990A
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frequency
new energy
equivalent
frequency modulation
unit
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毕天姝
葛辰雨
王程
胥国毅
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North China Electric Power University
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North China Electric Power University
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Abstract

The invention discloses a calculation method for decoupling an adjustable range of a frequency modulation parameter of a new energy power system, which belongs to the technical field of power system frequency control and comprises the following steps: s1, selecting a high-proportion new energy power system as a research object, wherein the new energy unit participates in frequency modulation through virtual inertia response and primary frequency modulation control; s2, taking the difference of dynamic response of the power supply into consideration, and constructing a system active-frequency dynamic model by adopting a transfer function; s3, considering limiting links of all units in the system, and establishing a linearization mathematical model of a dynamic equation of the frequency modulation process of the system; s4, solving a two-dimensional frequency modulation parameter safety domain taking each frequency modulation parameter as a coordinate axis through identifying vertexes; s5, considering the adjustable range of the frequency modulation parameters, constructing a two-dimensional frequency modulation parameter rectangular security domain with minimum frequency modulation cost, and realizing decoupling among all frequency modulation parameters. The method for calculating the decoupling of the adjustable range of the frequency modulation parameter of the new energy power system can solve the problem that the safety range of the frequency modulation parameter of the system is not clear.

Description

Calculation method for decoupling frequency modulation parameter adjustable range of new energy power system
Technical Field
The invention relates to the technical field of frequency control of power systems, in particular to a calculation method for decoupling an adjustable range of a frequency modulation parameter of a new energy power system.
Background
The frequency modulation parameters in the system are important indexes for determining the frequency stability of the power system, and the frequency modulation parameters among stations cooperate to jointly ensure the frequency stability of the system. With the large-scale access of new energy, especially tens of millions of kilowatt-level new energy bases and deep-open-sea wind power, the system frequency faces a greater risk of instability. If the frequency modulation parameters of part of stations in the system are located outside the safety domain, the maximum deviation value of the disturbed frequency change rate and frequency is increased, and the high-frequency switching-off and low-frequency load shedding of the system are triggered, so that a blackout accident can be possibly caused.
Therefore, the safety range of the frequency modulation parameters of each station is critical, so that the method not only can provide frequency instability risk early warning for power grid dispatching operators, but also can be used as an important reference index for real-time control after disturbance.
The frequency modulation parameter safety domain of each station in the current system is formulated according to national standards. However, with the advance of the dual-carbon target, the installed proportion and the generated energy of the new energy are improved, the auxiliary service market has certain requirements on the spare capacity provided by each new energy station, and standards and benefits are regulated for the rapid frequency response service such as virtual inertia, primary frequency modulation and the like, so that the provision of additional frequency control by each new energy station is promoted. In the case of a high proportion of new energy or uneven distribution of inertia at the receiving end, the safety range of the current frequency modulation parameters may no longer be applicable. The safety range of the frequency modulation parameters of the system is not clear, and the frequency stability of the system is restricted.
Therefore, a calculation method for decoupling the adjustable range of the frequency modulation parameter of the new energy power system is needed, so that the system frequency stability is ensured.
Disclosure of Invention
The invention aims to provide a calculation method for decoupling the adjustable range of the frequency modulation parameter of a new energy power system, which can solve the problem that the safety range of the frequency modulation parameter of the system is not clear, realize the optimization and the setting of the frequency modulation parameter of each station of the system and has field application value.
In order to achieve the above purpose, the invention provides a calculation method for decoupling the adjustable range of the frequency modulation parameter of a new energy power system, which comprises the following steps:
s1, selecting a high-proportion new energy power system as a research object, wherein the new energy unit participates in frequency modulation through virtual inertia response and primary frequency modulation control;
s2, taking the difference of dynamic response of the power supply into consideration, and constructing a system active-frequency dynamic model by adopting a transfer function;
s3, taking a synchronous unit and a limiting link of the new energy unit in the high-proportion new energy power system into consideration, and establishing a linearization mathematical model of a dynamic equation of the system frequency modulation process;
s4, solving a two-dimensional frequency modulation parameter safety domain taking each frequency modulation parameter as a coordinate axis through identifying vertexes;
s5, considering the adjustable range of the frequency modulation parameters, constructing a two-dimensional frequency modulation parameter rectangular security domain with minimum frequency modulation cost, and realizing decoupling among all frequency modulation parameters.
Preferably, in step S1, the grid of the high-proportion new energy power system is an ac grid, and the power supply includes a synchronous power supply and a new energy unit.
Preferably, in step S2, after the power disturbance occurs in the high-proportion new energy power system, the frequency dynamic response process is represented by a rocking equation:
wherein f 0 Rated frequency for the system; Δf is the system frequency deviation; h g The inertia of the system synchronous machine is adopted; d is a damping coefficient; ΔP m The per unit value of the mechanical power variation of each frequency modulation unit; ΔP e The per unit value of the active mutation quantity of the load;
the transfer function of equation (1) is expressed as:
-(2H g s+D)Δf(s)＝ΔP m (s)-ΔP e (s) (2)
wherein Δf(s) is the frequency domain form of the per unit value of the system frequency deviation; ΔP m (s) frequency domain form of per unit value of mechanical power variation of each frequency modulation unit；ΔP e (s) is a frequency domain version of the per unit value of the load active mutation quantity; s is the variation of the complex frequency domain;
the active power adjustment quantity of each frequency modulation unit is constrained by a dead zone link and an amplitude limiting link, and the dead zone link is ignored and only the influence of the amplitude limiting link on the frequency dynamic of the system is considered because the dead zone has small influence on the maximum deviation value of the frequency;
the method comprises the steps of performing equivalent aggregation on all synchronous machines in a high-proportion new energy power system to form equivalent synchronous units, wherein the turbine unit is regarded as a turbine unit with a reheating time constant of 0.5 times of a hydraulic hammer effect time constant and a high-pressure cylinder power proportion of-2;
For low-frequency disturbance, obtaining the mechanical power adjustment quantity of the equivalent synchronous unit, wherein the speed regulator limiting link of the equivalent synchronous unit is command limiting:
the mechanical power adjustment quantity of the equivalent synchronous unit under high-frequency disturbance is as follows:
wherein,the active limiting value is equivalent to that of the synchronous unit; />The active power of the equivalent synchronous machine set after the amplitude limiting link under the low-frequency disturbanceAdjusting the amount; />The active adjustment quantity of the equivalent synchronous unit under high-frequency disturbance after the amplitude limiting link is adopted; k (K) g The gain of a speed regulator of the equivalent synchronous unit; />The active adjustment quantity is output by the equivalent synchronous unit through the prime motor under low-frequency disturbance; />The active adjustment quantity is output by the equivalent synchronous unit through the prime motor under high-frequency disturbance; f (F) H The high-pressure turbine coefficient is the equivalent synchronous machine; t (T) R The reheating time constant is equivalent to that of the synchronous unit;
according to the virtual inertia and the primary frequency modulation modeling, frequency support provided by each new energy unit is connected, and the equivalence of each new energy unit in the system is aggregated into an equivalence new energy unit;
for low-frequency disturbance, obtaining the mechanical power adjustment quantity of the equivalent new energy unit;
the mechanical power adjustment quantity of the equivalent synchronous unit under high-frequency disturbance is as follows:
wherein,adding active power adjustment quantity of a frequency control link for the equivalent new energy unit under low-frequency disturbance; Adding active power adjustment quantity of a frequency control link for the equivalent new energy unit under high-frequency disturbance; h ne An inertial time constant of virtual inertia response of the equivalent new energy unit; k (K) ne The gain coefficient is the gain coefficient of primary frequency modulation control of the equivalent new energy unit; t (T) ne The control time constant of the first-order inertia link of the inverter of the equivalent new energy unit is set; virtual inertial response of equivalent new energy unit and primary frequency modulation control together use standby power, wherein +.>Is the active limiting value of the equivalent new source unit, < ->The active adjustment quantity of the equivalent new energy unit under low-frequency disturbance after the limiting link is adopted; />The active adjustment quantity of the equivalent new energy unit under high-frequency disturbance after the limiting link is adopted.
Preferably, in step S3, the frequency modulation process dynamic equation is discretized by a forward difference method, and a bilinear term in the frequency modulation process dynamic equation is linearized by a mccomick envelope, so as to respectively construct a linear model of the frequency response of the high-proportion new energy power system after low-frequency disturbance and high-frequency disturbance;
(1) A linear model of the frequency response of the high-proportion new energy power system after low-frequency disturbance:
(1) high-proportion new energy power system frequency deviation:
wherein,the occurrence of the low-frequency disturbance is delta P L System n under low frequency disturbance of (2) . 、n . -a frequency deviation of 1 step; d, d n For differential step length, H g The inertia time constant of the equivalent synchronous machine; p (P) L The total load of the new energy power system with high proportion is; />The active adjustment quantity of the nth-1 step length of the equivalent synchronous unit and the equivalent new energy unit under low-frequency disturbance is respectively calculated; f (f) 0 Rated frequency of a high-proportion new energy power system; s is S b The total capacity of the high-proportion new energy power system is obtained; />Is the rated capacity of the equivalent thermal power unit; />The rated capacity of the equivalent new energy unit; d is a system damping coefficient;
(2) active power adjustment quantity of equivalent synchronous unit:
wherein,for low-frequency disturbanceValue synchronization unit in nth . 、n . -an active adjustment amount output by 1 step; />Respectively, the nth system of the equivalent synchronous units under low-frequency disturbance after the speed regulator limiting link . 、n . -an active adjustment amount of 1 step; />The active limiting value and the rated capacity of the equivalent thermal power generating unit are respectively; k (K) g The gain of a speed regulator of the equivalent synchronous unit; t (T) R The reheating time constant is equivalent to that of the synchronous unit; f (F) H The high-pressure turbine coefficient is equal to the high-pressure turbine coefficient of the synchronous unit;
(3) active power adjustment quantity of equivalent new energy unit:
wherein,respectively, the nth system of the equivalent new energy unit under low-frequency disturbance after the inverter first-order inertia link . 、n . -a frequency offset value of 1 step; />The active adjustment quantity after the first-order inertia link and the active adjustment quantity after the amplitude limiting link of the equivalent new energy unit under the low-frequency disturbance are respectively; />The active limiting value and the rated capacity of the equivalent new energy unit are respectively; h ne The inertial time constant is equivalent to the inertial time constant of the new energy unit; k (K) ne The speed regulator gain of the equivalent new energy unit; t (T) ne The time constant of the first-order inertia link of the inverter of the equivalent new energy unit;
(2) A linear model of the frequency response of the high-proportion new energy power system after high-frequency disturbance:
wherein,the occurrence of the high-frequency disturbance is delta P L System under high frequency disturbance of (2)Frequency deviation of n.n. -1 steps; />Respectively the active adjustment quantity of the nth-1 step length of the equivalent synchronous unit and the equivalent new energy unit under high-frequency disturbance; />Respectively the nth equivalent synchronous units under high-frequency disturbance . 、n . -an active adjustment amount output by 1 step; />Respectively, the nth system of the equivalent synchronous units under high-frequency disturbance after the speed regulator limiting link . 、n . -an active adjustment amount of 1 step; />Respectively, the system n is after the equivalent new energy units under the high-frequency disturbance pass through the first-order inertia link of the inverter . 、n . -a frequency offset value of 1 step; / >The active adjustment quantity after the first-order inertia link and the active adjustment quantity after the limiting link of the equivalent new energy unit under the high-frequency disturbance are respectively;
(3) The initial state of the disturbed high-proportion new energy power system is as follows:
the disturbance comprises low-frequency disturbance and high-frequency disturbance, the high-proportion new energy power system normally operates before the disturbance occurs, the frequency of the high-proportion new energy power system is the rated frequency, the frequency deviation amount of the high-proportion new energy power system is 0 at the initial moment of the disturbance, the active adjustment amounts of the equivalent synchronous unit and the equivalent new energy unit are both 0, and the following constraint exists:
the equation (26) has a max/min operation function and bilinear terms, and the equation is solved by an equivalent processing method of the max/min operation function introduced in the limiting link and an McCormick envelope convex relaxation method introduced in the bilinear terms;
(1) equivalent synchronous unit and equivalent new energy unit amplitude limiting link in dynamic equation of frequency modulation process: the compact mathematical form of the equivalent synchronous unit and the equivalent new energy unit limiting link is expressed as y=min (x, a) or y=max (x, a), and the functional equivalent of the form as y=g (x) is expressed as:
wherein x and y are variables to be solved; g is the functional relation between the variables x and y;
For the amplitude limiting link of the equivalent synchronous unit, adding an objective function related to frequency deviation And the active adjustment quantity of the equivalent new energy unit after the first-order inertia link is +.> Then the constraint conditions comprising the min/max arithmetic function are equivalently transformed:
the governor clipping constraint is expressed equivalently in terms of a set of linear constraints:
(2) bilinear terms in the dynamic equation of the frequency modulation process: the bilinear term is the product term of two variables to be solved, and each bilinear term in the dynamic equation of the frequency modulation process is respectivelyWherein variables to be solved are respectively equal value new energy unit inertia time constant H ne Primary frequency modulation gain K of equivalent new energy unit ne And frequency deviation +.f. of nth step of system under low frequency disturbance and high frequency disturbance>Convex relaxation bilinear terms through the mccomick envelope; solving inertial time constant H of equivalent new energy unit ne Primary frequency modulation gain K of equivalent new energy unit ne The maximum and minimum values of (2) and (35) of the original objective function are eliminated, and the inertial time constant H of the equivalent new energy unit is respectively maximized and minimized under the original problem constraint formulas (11), (12), (14), (15), (16), (18), (20) to (22), (24) and (27) ne Primary frequency modulation gain K of equivalent new energy unit ne ；
Bilinear terms are linearized by the mccomick envelope:
Wherein x is i 、x j The independent variable to be solved;independent variables x to be solved i Minimum and maximum values of (2);independent variables x to be solved j Minimum and maximum values of (2); y is a dependent variable to be solved; c ij Is a constant coefficient; omega ij ＝x i x j For two independent variables x to be solved i 、x j Is a product term of (2);
order the
For low frequency disturbances, the following linear constraints are added:
and the equivalent substitution of formula (16) to:
wherein,respectively equal value new energy unit inertia time constant H ne Minimum and maximum of (2);respectively equal value new energy unit primary frequency modulation gain K ne Minimum and maximum of (2); />The system frequency deviation value of the nth step under the low-frequency disturbance is equal to the inertia time constant H of the new energy unit ne Is a product of (2); />The system frequency deviation value of the nth step under low-frequency disturbance and the inertia time constant K of the equivalent new energy unit ne Is a product of (2); />The maximum deviation value limit value of the system frequency under low-frequency disturbance is set;
for high frequency disturbances, the following linear constraints are added: :
and the equivalent substitution of formula (22) to:
wherein,the system frequency deviation value of the nth step under high-frequency disturbance and the inertia time constant H of the equivalent new energy unit ne Is a product of (2); />The system frequency deviation value of the nth step under high-frequency disturbance and the inertia time constant K of the equivalent new energy unit ne Is a product of (2); />The maximum deviation value limit value of the system frequency under high-frequency disturbance is set;
in order to ensure the stable frequency of the high-proportion new energy power system, the maximum deviation value of the frequency of the high-proportion new energy power system is required to be not more than a required given value, namely:
wherein,respectively the nth under the low-frequency disturbance and the high-frequency disturbance . System frequency offset values for the individual steps;the maximum deviation value limit value of the system frequency under the low-frequency disturbance and the high-frequency disturbance is respectively set.
Preferably, in step S4, because the dynamic equations of the frequency modulation process of the time domain discretization are all linear constraints, a frequency modulation parameter safety domain convex set is constructed; calculating a frequency modulation parameter safety domain through a PVE algorithm, firstly solving vertexes of the overall shape of the frequency modulation parameter safety domain, then expanding the existing vertex set, and calculating new vertexes beyond the current approximation value; the PVE algorithm objective function and constraints are as follows:
wherein α is a two-dimensional vector representing the direction of the identified vertex; h ne Virtual inertia time constant of the new energy unit with equivalent system; k (K) ne Primary frequency modulation gain coefficient of the system equivalent new energy unit;
the specific operation is as follows: firstly, enabling alpha to be the base of coordinate axes corresponding to two frequency modulation parameters respectively, further respectively obtaining frequency modulation parameter points corresponding to the maximum value and the minimum value of the two frequency modulation parameters, and further determining the basic shape of a frequency modulation parameter security domain; then, let alpha be the external normal vector of each side in the current safety domain approximation, thereby solving the current vertex set New vertices outside; let Deltah (i,k) The distance between the solved new vertex and the primary side of the safety domain approximation is calculated, wherein i is the number of circles around the safety domain approximation, and k is the number of the solved new vertex in one circle around the safety domain approximation; order D (i) ＝max{Δh (i,k) K is the maximum value of the distance between the new vertex and the primary side of the security domain approximation in one circle around the security domain approximation; if D (i) And not more than a pre-specified error margin epsilon, terminating the algorithm, and outputting the convex hull of the existing vertex as a frequency modulation parameter safety domain.
Preferably, in step S5, considering the adjustable range of the frequency modulation parameter, a two-dimensional frequency modulation parameter rectangular security domain with minimum frequency modulation cost is constructed, and decoupling among the frequency modulation parameters is realized, which comprises the following specific operations:
(1) Examining inscribed rectangles of the frequency modulation parameter security domain, and arranging all vertexes of the frequency modulation parameter security domain along the anticlockwise direction to form a vertex set V= { V i I=1.2, … N, where Vi is the ith vertex of the polygon and N is the number of polygon vertices; defining vertex vector alpha i I=1.2, … N is the vertex V i In a counter-clockwise direction to its next adjacent vertex V i+1 Wherein the vertex vector alpha N Is the vertex V N To the vertex V 1 Is a direction vector of (2);
(2) Constructing parallel clusters which are parallel to the longitudinal axis of the frequency modulation parameter safety domain and have two intersection points with the edges of the safety domain polygon, wherein the distance between adjacent parallel lines is a given value; for the ith parallel line, the two intersection points of the ith parallel line and the edge of the polygon are respectively I i,1 、I i,2 Through I i,1 、I i,2 The component signs of the vertex vectors of the frequency modulation parameter safety domain in the transverse axis direction are opposite; respectively pass through I i,1 、I i,2 Parallel lines are made in the same direction of the transverse axis of the frequency modulation parameter safety domain, and two intersection points I are respectively formed between the two parallel lines and the edges of the polygon i,4 、I i,3 Through I i,4 、I i,3 The component signs of the vertex vectors of the frequency modulation parameter safety domain in the transverse axis direction are opposite; i is as follows i,1 、I i,2 、I i,3 、I i,4 Forming inscribed rectangles of the frequency modulation parameter security domain for the vertexes;
(3) Sequentially substituting four vertexes of each inscribed rectangle in the frequency modulation parameter security domain into a Simulink model for inspection, if a certain vertex does not meet the frequency stability requirement, enabling the vertex to be compressed inwards along a connecting line of the vertex and the center of gravity of the inscribed rectangle until the frequency modulation parameter value corresponding to the vertex meets the frequency stability constraint condition, and adjusting coordinates of two adjacent vertexes according to the updated vertex to form a decoupling rectangle meeting the frequency stability constraint;
(4) Considering that the frequency modulation cost corresponding to the frequency modulation parameter is minimum, and measuring the average frequency modulation cost corresponding to the current frequency modulation parameter adjustable range by means of the average frequency modulation cost corresponding to the four vertexes of the decoupling rectangle in the frequency modulation parameter safety domain.
Therefore, the calculation method for decoupling the adjustable range of the frequency modulation parameter of the new energy power system has the following technical effects:
(1) The method provided by the invention realizes the frequency modulation parameter safety domain calculation of each station in the system based on the improved frequency response model, and decouples the adjustable range among the frequency modulation parameters.
(2) The frequency response model adopted by the invention considers the virtual inertia and sagging control of the new energy unit, considers nonlinear links such as clipping, first-order inertia time constant and the like of each unit, and more truly describes the frequency response process after disturbance.
(3) On the premise of guaranteeing the system frequency stability, the frequency modulation parameter safety domain calculation of the new energy power system comprehensively considers the adjustable range of the frequency modulation parameter and the frequency modulation cost, and realizes decoupling of the frequency modulation parameters, so that each frequency modulation parameter is independently set in the adjustable range of the frequency modulation parameter, and is not influenced by the values of other frequency modulation parameters.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a high-proportion new energy power system frequency response model;
FIG. 3 is a schematic illustration of a PVE algorithm;
FIG. 4 is a flowchart of an adjustable range decoupling algorithm between frequency modulation parameters;
FIG. 5 is a schematic diagram of an inscribed rectangle solving algorithm in a frequency modulation parameter safety domain;
FIG. 6 is a schematic diagram of a decoupling rectangular solution algorithm in a frequency modulation parameter safety domain considering frequency stabilization;
FIG. 7 is a solution result of the security domain of the FM parameter of the three-machine system according to the embodiment;
FIG. 8 is a decoupling solution result for the tuning range of the tuning parameters of the three-machine system according to the embodiment.
Detailed Description
The technical scheme of the invention is further described below through the attached drawings and the embodiments.
Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.
Example 1
As shown in fig. 1, a flowchart of a method for calculating decoupling of adjustable range of frequency modulation parameters of a new energy power system is provided, which includes the following steps:
s1, selecting a high-proportion new energy power system as a research object, wherein the new energy unit participates in frequency modulation through virtual inertia response and primary frequency modulation control.
As shown in fig. 2, the frequency response model of the high-ratio new energy power system is shown. The generator in the system comprises a synchronous unit and a new energy unit, wherein the new energy unit comprises wind power and photovoltaic. The high-proportion new energy power system grid is an alternating current power grid, the power supply comprises a synchronous power supply and a new energy unit, the new energy unit participates in frequency modulation through virtual inertia and primary frequency modulation control, and the load is a constant power load.
S2, taking the difference of dynamic response of the power supply into consideration, and constructing a system active-frequency dynamic model by adopting a transfer function;
after the high-proportion new energy power system generates power disturbance, the frequency dynamic response process is represented by a swinging equation:
wherein f 0 Rated frequency for the system; Δf is the system frequency deviation; h g The inertia of the system synchronous machine is adopted; d is a damping coefficient; ΔP m The per unit value of the mechanical power variation of each frequency modulation unit; ΔP e The per unit value of the active mutation quantity of the load;
the transfer function of equation (1) is expressed as:
-(2H g s+D)Δf(s)＝ΔP m (s)-ΔP e (s) (2)
wherein Δf(s) is the frequency domain form of the per unit value of the system frequency deviation; ΔP m (s) is a frequency domain form of per unit value of the mechanical power variation of each frequency modulation unit; ΔP e (s) is a frequency domain version of the per unit value of the load active mutation quantity; s is the variation of the complex frequency domain;
the active power adjustment quantity of each frequency modulation unit is constrained by a dead zone link and an amplitude limiting link, and the dead zone link is ignored and only the influence of the amplitude limiting link on the frequency dynamic of the system is considered because the dead zone has small influence on the maximum deviation value of the frequency;
the method comprises the steps of performing equivalent aggregation on all synchronous machines in a high-proportion new energy power system to form equivalent synchronous units, wherein the turbine unit is regarded as a turbine unit with a reheating time constant of 0.5 times of a hydraulic hammer effect time constant and a high-pressure cylinder power proportion of-2;
For low-frequency disturbance, obtaining the mechanical power adjustment quantity of the equivalent synchronous unit, wherein the speed regulator limiting link of the equivalent synchronous unit is command limiting:
the mechanical power adjustment quantity of the equivalent synchronous unit under high-frequency disturbance is as follows:
wherein,the active limiting value is equivalent to that of the synchronous unit; />The active adjustment quantity of the equivalent synchronous unit under low-frequency disturbance after the amplitude limiting link is adopted; />The active adjustment quantity of the equivalent synchronous unit under high-frequency disturbance after the amplitude limiting link is adopted; k (K) g The gain of a speed regulator of the equivalent synchronous unit; />The active adjustment quantity is output by the equivalent synchronous unit through the prime motor under low-frequency disturbance; />The active adjustment quantity is output by the equivalent synchronous unit through the prime motor under high-frequency disturbance; f (F) H The high-pressure turbine coefficient is the equivalent synchronous machine; t (T) R The reheating time constant is equivalent to that of the synchronous unit;
according to the virtual inertia and the primary frequency modulation modeling, frequency support provided by each new energy unit is connected, and the equivalence of each new energy unit in the system is aggregated into an equivalence new energy unit;
for low-frequency disturbance, obtaining the mechanical power adjustment quantity of the equivalent new energy unit;
the mechanical power adjustment quantity of the equivalent synchronous unit under high-frequency disturbance is as follows:
wherein,adding active power adjustment quantity of a frequency control link for the equivalent new energy unit under low-frequency disturbance; Adding active power adjustment quantity of a frequency control link for the equivalent new energy unit under high-frequency disturbance; h ne An inertial time constant of virtual inertia response of the equivalent new energy unit; k (K) ne The gain coefficient is the gain coefficient of primary frequency modulation control of the equivalent new energy unit; t (T) ne The control time constant of the first-order inertia link of the inverter of the equivalent new energy unit is set; virtual inertial response of equivalent new energy unit and primary frequency modulation control together use standby power, wherein +.>Is the active limiting value of the equivalent new source unit, < ->The active adjustment quantity of the equivalent new energy unit under low-frequency disturbance after the limiting link is adopted; />Equivalent new energy under high-frequency disturbanceActive adjustment quantity of the source unit after the amplitude limiting link.
S3, taking a synchronous unit and a limiting link of the new energy unit in the high-proportion new energy power system into consideration, and establishing a linearization mathematical model of a dynamic equation of the system frequency modulation process;
discretizing a dynamic equation of the frequency modulation process by a forward difference method, and respectively constructing a linear model of the frequency response of the high-proportion new energy power system after low-frequency disturbance and high-frequency disturbance by using bilinear terms in the dynamic equation of the frequency modulation process by McCormick envelope linearization;
(1) A linear model of the frequency response of the high-proportion new energy power system after low-frequency disturbance:
(1) High-proportion new energy power system frequency deviation:
wherein,the occurrence of the low-frequency disturbance is delta P L System n under low frequency disturbance of (2) . 、n . -a frequency deviation of 1 step; d, d n For differential step length, H g The inertia time constant of the equivalent synchronous machine; p (P) L The total load of the new energy power system with high proportion is; />The active adjustment quantity of the nth-1 step length of the equivalent synchronous unit and the equivalent new energy unit under low-frequency disturbance is respectively calculated; f (f) 0 Rated frequency of a high-proportion new energy power system; s is S b The total capacity of the high-proportion new energy power system is obtained; />Is equal toRated capacity of thermal power generating unit is calculated; />The rated capacity of the equivalent new energy unit; d is a system damping coefficient;
(2) active power adjustment quantity of equivalent synchronous unit:
wherein,is the nth equivalent synchronous unit under low-frequency disturbance . 、n . -an active adjustment amount output by 1 step; />Respectively, the nth system of the equivalent synchronous units under low-frequency disturbance after the speed regulator limiting link . 、n . -an active adjustment amount of 1 step; />The active limiting value and the rated capacity of the equivalent thermal power generating unit are respectively; k (K) g The gain of a speed regulator of the equivalent synchronous unit; t (T) R The reheating time constant is equivalent to that of the synchronous unit; f (F) H The high-pressure turbine coefficient is equal to the high-pressure turbine coefficient of the synchronous unit;
(3) Active power adjustment quantity of equivalent new energy unit:
wherein,respectively, the nth system of the equivalent new energy unit under low-frequency disturbance after the inverter first-order inertia link . 、n . -a frequency offset value of 1 step; />The active adjustment quantity after the first-order inertia link and the active adjustment quantity after the amplitude limiting link of the equivalent new energy unit under the low-frequency disturbance are respectively; />The active limiting value and the rated capacity of the equivalent new energy unit are respectively; h ne The inertial time constant is equivalent to the inertial time constant of the new energy unit; k (K) ne The speed regulator gain of the equivalent new energy unit; t (T) ne The time constant of the first-order inertia link of the inverter of the equivalent new energy unit;
(2) A linear model of the frequency response of the high-proportion new energy power system after high-frequency disturbance:
wherein,the occurrence of the high-frequency disturbance is delta P L System n under high frequency disturbance of (2) . 、n . -a frequency deviation of 1 step; />Respectively the active adjustment quantity of the nth-1 step length of the equivalent synchronous unit and the equivalent new energy unit under high-frequency disturbance; />Respectively the nth equivalent synchronous units under high-frequency disturbance . 、n . -an active adjustment amount output by 1 step; />Respectively, the nth system of the equivalent synchronous units under high-frequency disturbance after the speed regulator limiting link . 、n . -an active adjustment amount of 1 step; / >Respectively obtaining the frequency deviation values of the nth and the n-1 step of the system after the equivalent new energy unit under the high-frequency disturbance passes through the first-order inertia link of the inverter; />The active adjustment quantity after the first-order inertia link and the active adjustment quantity after the limiting link of the equivalent new energy unit under the high-frequency disturbance are respectively;
(3) The initial state of the disturbed high-proportion new energy power system is as follows:
the disturbance comprises low-frequency disturbance and high-frequency disturbance, the high-proportion new energy power system normally operates before the disturbance occurs, the frequency of the high-proportion new energy power system is the rated frequency, the frequency deviation amount of the high-proportion new energy power system is 0 at the initial moment of the disturbance, the active adjustment amounts of the equivalent synchronous unit and the equivalent new energy unit are both 0, and the following constraint exists:
the equation (26) has a max/min operation function and bilinear terms, and the equation is solved by an equivalent processing method of the max/min operation function introduced in the limiting link and an McCormick envelope convex relaxation method introduced in the bilinear terms;
(1) equivalent synchronous unit and equivalent new energy unit amplitude limiting link in dynamic equation of frequency modulation process: the compact mathematical form of the equivalent synchronous unit and the equivalent new energy unit limiting link is expressed as y=min (x, a) or y=max (x, a), and the functional equivalent of the form as y=g (x) is expressed as:
Wherein x and y are variables to be solved; g is the functional relation between the variables x and y;
for the amplitude limiting link of the equivalent synchronous unit, adding an objective function related to frequency deviation And the active adjustment quantity of the equivalent new energy unit after the first-order inertia link is +.> Then the constraint conditions comprising the min/max arithmetic function are equivalently transformed:
the governor clipping constraint is expressed equivalently in terms of a set of linear constraints:
(2) bilinear terms in the dynamic equation of the frequency modulation process: the bilinear term is the product term of two variables to be solved, and each bilinear term in the dynamic equation of the frequency modulation process is respectivelyWherein variables to be solved are respectively equal value new energy unit inertia time constant H ne Primary frequency modulation gain K of equivalent new energy unit ne And frequency deviation +.f. of nth step of system under low frequency disturbance and high frequency disturbance>Convex relaxation bilinear terms through the mccomick envelope; solving inertial time constant H of equivalent new energy unit ne Primary frequency modulation gain K of equivalent new energy unit ne The maximum and minimum values of (2) and (35) of the original objective function are eliminated, and the inertial time constant H of the equivalent new energy unit is respectively maximized and minimized under the original problem constraint formulas (11), (12), (14), (15), (16), (18), (20) to (22), (24) and (27) ne Primary frequency modulation gain K of equivalent new energy unit ne ；
Bilinear terms are linearized by the mccomick envelope:
wherein x is i 、x j The independent variable to be solved;independent variables x to be solved i Minimum and maximum values of (2);independent variables x to be solved j Minimum and maximum values of (2); y is a dependent variable to be solved; c ij Is a constant coefficient; omega ij ＝x i x j For two independent variables x to be solved i 、x j Is a product term of (2);
order the
For low frequency disturbances, the following linear constraints are added:
(29)
and the equivalent substitution of formula (16) to:
wherein,respectively equal value new energy unit inertia time constant H ne Minimum and maximum of (2);respectively equal value new energy unit primary frequency modulation gain K ne Minimum and maximum of (2); />The system frequency deviation value of the nth step under the low-frequency disturbance is equal to the inertia time constant H of the new energy unit ne Is a product of (2); />The system frequency deviation value of the nth step under low-frequency disturbance and the inertia time constant K of the equivalent new energy unit ne Is a product of (2); />The maximum deviation value limit value of the system frequency under low-frequency disturbance is set;
for high frequency disturbances, the following linear constraints are added: :
and the equivalent substitution of formula (22) to:
wherein,the system frequency deviation value of the nth step under high-frequency disturbance and the inertia time constant H of the equivalent new energy unit ne Is a product of (2); />The system frequency deviation value of the nth step under high-frequency disturbance and the inertia time constant K of the equivalent new energy unit ne Is a product of (2); />The maximum deviation value limit value of the system frequency under high-frequency disturbance is set;
in order to ensure the stable frequency of the high-proportion new energy power system, the maximum deviation value of the frequency of the high-proportion new energy power system is required to be not more than a required given value, namely:
wherein,the system frequency deviation values of the nth step under the low-frequency disturbance and the high-frequency disturbance are respectively;the maximum deviation value limit value of the system frequency under the low-frequency disturbance and the high-frequency disturbance is respectively set.
S4, solving a two-dimensional frequency modulation parameter safety domain taking each frequency modulation parameter as a coordinate axis through identifying vertexes;
because the dynamic equations of the frequency modulation process of the time domain discretization are all linear constraints, a frequency modulation parameter safety domain convex set is constructed; calculating a frequency modulation parameter safety domain through a PVE algorithm, firstly solving vertexes of the overall shape of the frequency modulation parameter safety domain, then expanding the existing vertex set, and calculating new vertexes beyond the current approximation value; the PVE algorithm objective function and constraints are as follows:
wherein α is a two-dimensional vector representing the direction of the identified vertex; h ne Virtual inertia time constant of the new energy unit with equivalent system; k (K) ne Primary frequency modulation gain coefficient of the system equivalent new energy unit;
the specific operation is as follows: firstly, enabling alpha to be the base of coordinate axes corresponding to two frequency modulation parameters respectively, further respectively obtaining frequency modulation parameter points corresponding to the maximum value and the minimum value of the two frequency modulation parameters, and further determining the basic shape of a frequency modulation parameter security domain; then, alpha is respectively made to be the external normal vector of each side in the current safety domain approximation value, so that new vertexes outside the current vertex set are solved; let Deltah (i,k) The distance between the solved new vertex and the primary side of the safety domain approximation is calculated, wherein i is the number of circles around the safety domain approximation, and k is the number of the solved new vertex in one circle around the safety domain approximation; order D (i) ＝max{Δh (i,k) K is the maximum value of the distance between the new vertex and the primary side of the security domain approximation in one circle around the security domain approximation; if D (i) And not more than a pre-specified error margin epsilon, terminating the algorithm, and outputting the convex hull of the existing vertex as a frequency modulation parameter safety domain. FIG. 3 is a schematic diagram of PVE algorithm, as shown in FIG. 3, wherein the inertia time constant H and the primary frequency modulation gain K are two frequency modulation parameters to be solved,and the frequency modulation parameter points are corresponding to the maximum value of K, the maximum value of H, the minimum value of K and the minimum value of H respectively.New vertices, Δh, are extended for the first week around the frequency modulation parameter safety domain approximation (1,1) 、Δh (1,2) 、Δh (1,3) 、Δh (1,4) Is->Distance from the primary side of the security domain approximation, D (1) Is delta h (1,k) K is the maximum value in K.
S5, considering the adjustable range of the frequency modulation parameters, constructing a two-dimensional frequency modulation parameter rectangular security domain with minimum frequency modulation cost, and realizing decoupling among all frequency modulation parameters.
The adjustable range and economy of the frequency modulation parameters are considered, so that each frequency modulation parameter is independently set in the adjustable range and is not influenced by the values of other frequency modulation parameters. The basic idea of the algorithm is to examine each inscribed rectangle of the polygon of the frequency modulation parameter safety domain, and gradually reduce the adjustable range of the two frequency modulation parameters until the adjustable range meets the system frequency stability constraint. On the premise of guaranteeing the system frequency stability, a decoupling rectangle in a safety domain with minimum frequency modulation cost is selected, and further decoupling of the frequency modulation parameter adjustable range is achieved. FIG. 4 is a flowchart of an adjustable range decoupling algorithm between frequency modulation parameters, comprising the steps of:
(1) Let us examine inscribed rectangles of the security domain of the frequency modulation parameters. Arranging the vertexes of the frequency modulation parameter security domain along the anticlockwise direction to form a vertex set V= { V i I=1.2, … N }, where V i Is the ith vertex of the polygon, and N is the number of polygon vertices. Defining vertex vector alpha i I=1.2, … N is the vertex V i In a counter-clockwise direction to its next adjacent vertex V i+1 Wherein the vertex vector alpha N Is the vertex V N To the vertex V 1 Is a direction vector of (a).
(2) And constructing parallel clusters which are parallel to the longitudinal axis of the frequency modulation parameter safety domain and have two intersecting points with the edges of the safety domain polygon, wherein the distance between adjacent parallel lines is a given value. For the ith parallel line, the two intersection points of the ith parallel line and the edge of the polygon are respectively I i,1 、I i,2 Respectively examine I i,1 、I i,2 And the sign of the component in the transverse axis direction of the frequency modulation parameter security domain is opposite. Respectively pass through I i,1 、I i,2 Directional frequency modulation parameter settingThe same direction of the global transverse axis is parallel, and two intersection points I are respectively formed between the global transverse axis and the polygon side i,4 、I i,3 Through I i,4 、I i,3 The component signs of the vertex vectors of the frequency modulation parameter safety domain in the transverse axis direction are opposite. I is as follows i,1 、I i,2 、I i,3 、I i,4 Inscribed rectangles of the frequency modulation parameter security domain are constructed for vertices. Fig. 5 is a schematic diagram of an algorithm for solving an inscribed rectangle in a frequency modulation parameter safety domain, where the longitudinal edges of the inscribed rectangle and the polygon with two intersections in the two frequency modulation parameter safety domains may be the left longitudinal edge and the right longitudinal edge of the inscribed rectangle, respectively.
(3) And substituting four vertexes of each inscribed rectangle in the frequency modulation parameter security domain into the Simulink model in sequence for inspection, if a certain vertex does not meet the frequency stability requirement, enabling the vertex to be compressed inwards along a connecting line of the vertex and the center of gravity of the inscribed rectangle until the vertex meets the frequency stability constraint condition, and adjusting coordinates of two adjacent vertexes according to the updated vertex to form a decoupling rectangle meeting the frequency stability constraint. Fig. 6 is a schematic diagram of a solution algorithm of a decoupling rectangle in a frequency modulation parameter safety domain considering frequency stabilization, wherein the vertex of the inscribed rectangle in the second quadrant and the vertex of the fourth quadrant do not meet the frequency stabilization requirement, so that the vertex is respectively compressed inwards along the connection line of the vertex and the center of gravity of the inscribed rectangle, and the decoupling rectangle meeting the frequency stabilization in the frequency modulation parameter safety domain is obtained.
(4) Consider that the frequency modulation cost corresponding to the frequency modulation parameter is minimum. And measuring the average frequency modulation cost corresponding to the current frequency modulation parameter adjustable range by decoupling the average frequency modulation cost corresponding to the four vertexes of the rectangle in the frequency modulation parameter safety domain.
The new energy unit frequency modulation cost is calculated according to the compensation standard of virtual inertia and primary frequency modulation in northeast areas, the primary frequency modulation auxiliary service of wind power compensates according to 100 yuan/kilowatt hour, and virtual inertia response compensates according to 50 yuan/kilowatt hour. Substituting the frequency modulation parameters corresponding to the decoupling rectangular vertexes of each frequency modulation parameter safety domain into a system Simulink model to simulate under expected faults, examining the generated energy of each station respectively from the initial disturbance moment to the time when the system frequency deviation value reaches the maximum value, and calculating the frequency modulation cost according to the compensation standard.
The method according to the invention is illustrated by means of the following specific examples.
The embodiment of the invention comprises 3 generators, wherein G1 and G2 are synchronous generators, G3 is a new energy unit controlled by a virtual synchronous machine, and the additional frequency control mode is virtual inertia and primary frequency modulation. The parameters of the system are shown in table 1.
Table 1 generator parameters
Setting the active disturbance in the system as low-frequency disturbance with the size of 120MW; the maximum deviation value limit value of the frequency is 0.5Hz; the system damping coefficient is 0.05p.u.; the active load of the system is 900MW.
The method comprises the following specific steps:
s1, selecting a high-proportion new energy power system as a research object, wherein the new energy unit participates in frequency modulation through virtual inertia response and primary frequency modulation control. For the three-machine system in the embodiment of the invention, the new energy capacity is 46.7 percent.
S2, taking the difference of dynamic response of the power supply into consideration, and constructing a system active-frequency dynamic model by adopting a transfer function.
S3, considering limiting links of all units in the system, and establishing a linearization mathematical model of a dynamic equation of the frequency modulation process of the system, wherein the discretization step length of the frequency dynamic equation is set to be 0.05.
And S4, solving a two-dimensional frequency modulation parameter safety domain taking each frequency modulation parameter as a coordinate axis through identifying the vertex. As shown in fig. 7, the solution result of the frequency modulation parameter safety domain of the three-machine system in this embodiment is that the system does not meet the frequency stability requirement when the virtual inertia time constant and the primary frequency modulation gain of the new energy unit G3 are both smaller.
S5, considering the adjustable range of the frequency modulation parameters, constructing a two-dimensional frequency modulation parameter rectangular security domain with minimum frequency modulation cost, and realizing decoupling among all frequency modulation parameters. As shown in FIG. 8, the frequency modulation parameter adjustable range decoupling method for the three-machine system according to the present embodiment As a result, when the virtual inertia time constant H of the new energy unit G3 ne ∈[0.1,27.8516]s, primary frequency modulation gain K ne ∈[10.2919,50]And when in p.u., the system meets the frequency modulation cost on the premise of guaranteeing the frequency stability requirement. The decoupled security domain of the frequency modulation parameters realizes decoupling among the frequency modulation parameters, so that each frequency modulation parameter is independently set in the adjustable range of the frequency modulation parameter and is not influenced by the values of other frequency modulation parameters.
Therefore, the calculation method for decoupling the adjustable range of the frequency modulation parameter of the new energy power system can solve the problem that the safety range of the frequency modulation parameter of the system is not clear, realizes the optimized setting of the frequency modulation parameter of each station of the system, and has field application value.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention and not for limiting it, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that: the technical scheme of the invention can be modified or replaced by the same, and the modified technical scheme cannot deviate from the spirit and scope of the technical scheme of the invention.

Claims (6)

1. The calculation method for decoupling the adjustable range of the frequency modulation parameter of the new energy power system is characterized by comprising the following steps of:
S1, selecting a high-proportion new energy power system as a research object, wherein the new energy unit participates in frequency modulation through virtual inertia response and primary frequency modulation control;
s2, taking the difference of dynamic response of the power supply into consideration, and constructing a system active-frequency dynamic model by adopting a transfer function;
s3, taking a synchronous unit and a limiting link of the new energy unit in the high-proportion new energy power system into consideration, and establishing a linearization mathematical model of a dynamic equation of the system frequency modulation process;
s4, solving a two-dimensional frequency modulation parameter safety domain taking each frequency modulation parameter as a coordinate axis through identifying vertexes;
s5, considering the adjustable range of the frequency modulation parameters, constructing a two-dimensional frequency modulation parameter rectangular security domain with minimum frequency modulation cost, and realizing decoupling among all frequency modulation parameters.
2. The method for calculating the decoupling of the adjustable range of the frequency modulation parameter of the new energy power system according to claim 1, wherein in the step S1, the high-proportion new energy power system grid is an ac power grid, and the power supply comprises a synchronous power supply and a new energy unit.
3. The method for calculating the decoupling of the adjustable range of the frequency modulation parameter of the new energy power system according to claim 2, wherein in step S2, after the power disturbance occurs in the high-ratio new energy power system, the frequency dynamic response process is represented by a rocking equation:
Wherein f 0 Rated frequency for the system; Δf is the system frequency deviation; h g The inertia of the system synchronous machine is adopted; d is a damping coefficient; ΔP m The per unit value of the mechanical power variation of each frequency modulation unit; ΔP e The per unit value of the active mutation quantity of the load;
the transfer function of equation (1) is expressed as:
-(2H g s+D)Δf(s)＝ΔP m (s)-ΔP e (s) (2)
wherein Δf(s) is the frequency domain form of the per unit value of the system frequency deviation; ΔP m (s) is a frequency domain form of per unit value of the mechanical power variation of each frequency modulation unit; ΔP e (s) is a frequency domain version of the per unit value of the load active mutation quantity; s is the variation of the complex frequency domain;
the active power adjustment quantity of each frequency modulation unit is constrained by a dead zone link and an amplitude limiting link, and the dead zone link is ignored and only the influence of the amplitude limiting link on the frequency dynamic of the system is considered because the dead zone has small influence on the maximum deviation value of the frequency;
the method comprises the steps of performing equivalent aggregation on all synchronous machines in a high-proportion new energy power system to form equivalent synchronous units, wherein the turbine unit is regarded as a turbine unit with a reheating time constant of 0.5 times of a hydraulic hammer effect time constant and a high-pressure cylinder power proportion of-2;
for low-frequency disturbance, obtaining the mechanical power adjustment quantity of the equivalent synchronous unit, wherein the speed regulator limiting link of the equivalent synchronous unit is command limiting:
The mechanical power adjustment quantity of the equivalent synchronous unit under high-frequency disturbance is as follows:
wherein,the active limiting value is equivalent to that of the synchronous unit; />The active adjustment quantity of the equivalent synchronous unit under low-frequency disturbance after the amplitude limiting link is adopted; />The active adjustment quantity of the equivalent synchronous unit under high-frequency disturbance after the amplitude limiting link is adopted; k (K) g The gain of a speed regulator of the equivalent synchronous unit; />The active adjustment quantity is output by the equivalent synchronous unit through the prime motor under low-frequency disturbance;the active adjustment quantity is output by the equivalent synchronous unit through the prime motor under high-frequency disturbance; f (F) H The high-pressure turbine coefficient is the equivalent synchronous machine; t (T) R The reheating time constant is equivalent to that of the synchronous unit;
according to the virtual inertia and the primary frequency modulation modeling, frequency support provided by each new energy unit is connected, and the equivalence of each new energy unit in the system is aggregated into an equivalence new energy unit;
for low-frequency disturbance, obtaining the mechanical power adjustment quantity of the equivalent new energy unit;
the mechanical power adjustment quantity of the equivalent synchronous unit under high-frequency disturbance is as follows:
wherein,adding active power adjustment quantity of a frequency control link for the equivalent new energy unit under low-frequency disturbance; />Adding active power adjustment quantity of a frequency control link for the equivalent new energy unit under high-frequency disturbance; h ne An inertial time constant of virtual inertia response of the equivalent new energy unit; k (K) ne The gain coefficient is the gain coefficient of primary frequency modulation control of the equivalent new energy unit; t (T) ne The control time constant of the first-order inertia link of the inverter of the equivalent new energy unit is set; virtual inertial response of equivalent new energy unit and primary frequency modulation control together use standby power, wherein +.>Is the active limiting value of the equivalent new source unit, < ->The active adjustment quantity of the equivalent new energy unit under low-frequency disturbance after the limiting link is adopted; />The active adjustment quantity of the equivalent new energy unit under high-frequency disturbance after the limiting link is adopted.
4. The method for calculating the frequency modulation parameter adjustable range decoupling of the new energy power system according to claim 3, wherein in the step S3, a dynamic equation of a frequency modulation process is discretized by a forward difference method, and a bilinear term in the dynamic equation of the frequency modulation process is linearized by an McCormick envelope, so that a linear model of frequency response of the new energy power system after low-frequency disturbance and high-frequency disturbance is respectively constructed;
(1) A linear model of the frequency response of the high-proportion new energy power system after low-frequency disturbance:
(1) high-proportion new energy power system frequency deviation:
wherein,the occurrence of the low-frequency disturbance is delta P L The frequency deviation of the n.n. -1 step of the system under the low frequency disturbance; d, d n For differential step length, H g The inertia time constant of the equivalent synchronous machine; p (P) L The total load of the new energy power system with high proportion is; />The active adjustment quantity of the nth-1 step length of the equivalent synchronous unit and the equivalent new energy unit under low-frequency disturbance is respectively calculated; f (f) 0 Rated frequency of a high-proportion new energy power system; s is S b The total capacity of the high-proportion new energy power system is obtained;is the rated capacity of the equivalent thermal power unit; />The rated capacity of the equivalent new energy unit; d is a system damping coefficient;
(2) active power adjustment quantity of equivalent synchronous unit:
wherein,the active adjustment quantity is output by the equivalent synchronous unit at the nth step and the n-1 th step under the low-frequency disturbance; />Respectively the active adjustment amounts of the nth step length and the n-1 th step length of the system after the equivalent synchronous machine set under low-frequency disturbance passes through the limiter link of the speed regulator; />The active limiting value and the rated capacity of the equivalent thermal power generating unit are respectively; k (K) g The gain of a speed regulator of the equivalent synchronous unit; t (T) R The reheating time constant is equivalent to that of the synchronous unit; f (F) H The high-pressure turbine coefficient is equal to the high-pressure turbine coefficient of the synchronous unit;
(3) active power adjustment quantity of equivalent new energy unit:
wherein,respectively obtaining frequency deviation values of the nth step and the n-1 th step of the system after the equivalent new energy unit under low-frequency disturbance passes through the first-order inertia link of the inverter; / >Respectively the active adjustment quantity of the low-frequency disturbance time-equivalent new energy unit after the first-order inertia link and the amplitude limiting ringThe active power adjustment after the section; />The active limiting value and the rated capacity of the equivalent new energy unit are respectively; h ne The inertial time constant is equivalent to the inertial time constant of the new energy unit; k (K) ne The speed regulator gain of the equivalent new energy unit; t (T) ne The time constant of the first-order inertia link of the inverter of the equivalent new energy unit;
(2) A linear model of the frequency response of the high-proportion new energy power system after high-frequency disturbance:
wherein the method comprises the steps of，The occurrence of the high-frequency disturbance is delta P L The frequency deviation of the nth step length and the n-1 step length of the system under the high-frequency disturbance; />Respectively the active adjustment quantity of the nth-1 step length of the equivalent synchronous unit and the equivalent new energy unit under high-frequency disturbance; />Respectively the active adjustment amounts output by the equivalent synchronous units under the high-frequency disturbance at the n-1 th step length; />Respectively the active adjustment amounts of the nth step length and the n-1 th step length of the system after the equivalent synchronous machine set under high-frequency disturbance passes through the limiter link of the speed regulator; />Respectively obtaining frequency deviation values of the nth step and the n-1 th step of the system after the equivalent new energy unit under high-frequency disturbance passes through the first-order inertia link of the inverter; />The active adjustment quantity after the first-order inertia link and the active adjustment quantity after the limiting link of the equivalent new energy unit under the high-frequency disturbance are respectively;
(3) The initial state of the disturbed high-proportion new energy power system is as follows:
the disturbance comprises low-frequency disturbance and high-frequency disturbance, the high-proportion new energy power system normally operates before the disturbance occurs, the frequency of the high-proportion new energy power system is the rated frequency, the frequency deviation amount of the high-proportion new energy power system is 0 at the initial moment of the disturbance, the active adjustment amounts of the equivalent synchronous unit and the equivalent new energy unit are both 0, and the following constraint exists:
the equation (26) has a max/min operation function and bilinear terms, and the equation is solved by an equivalent processing method of the max/min operation function introduced in the limiting link and an McCormick envelope convex relaxation method introduced in the bilinear terms;
(1) equivalent synchronous unit and equivalent new energy unit amplitude limiting link in dynamic equation of frequency modulation process: the compact mathematical form of the equivalent synchronous unit and the equivalent new energy unit limiting link is expressed as y=min (x, a) or y=max (x, a), and the functional equivalent of the form as y=g (x) is expressed as:
wherein x and y are variables to be solved; g is the functional relation between the variables x and y;
for the amplitude limiting link of the equivalent synchronous unit, adding an objective function related to frequency deviation And the active adjustment quantity of the equivalent new energy unit after the first-order inertia link is +. > Then the constraint conditions comprising the min/max arithmetic function are equivalently transformed:
the governor clipping constraint is expressed equivalently in terms of a set of linear constraints:
(2) bilinear terms in the dynamic equation of the frequency modulation process: the bilinear term is the product term of two variables to be solved, and each bilinear term in the dynamic equation of the frequency modulation process is respectivelyWherein variables to be solved are respectively equal value new energy unit inertia time constant H ne Primary frequency modulation gain K of equivalent new energy unit ne And the frequency deviation of the nth step of the system under low-frequency disturbance and high-frequency disturbance +.>Convex relaxation bilinear terms through the mccomick envelope; solving inertial time constant H of equivalent new energy unit ne Primary frequency modulation gain K of equivalent new energy unit ne The maximum and minimum values of (2) and (35) of the original objective function are eliminated, and the inertial time constant H of the equivalent new energy unit is respectively maximized and minimized under the original problem constraint formulas (11), (12), (14), (15), (16), (18), (20) to (22), (24) and (27) ne Primary frequency modulation gain K of equivalent new energy unit ne ；
Bilinear terms are linearized by the mccomick envelope:
wherein x is i 、x j The independent variable to be solved;independent variables x to be solved i Minimum and maximum values of (2);independent variables x to be solved j Minimum and maximum values of (2); y is a dependent variable to be solved; c ij Is a constant coefficient; omega ij ＝x i x j For two independent variables x to be solved i 、x j Is a product term of (2);
order the
For low frequency disturbances, the following linear constraints are added:
and the equivalent substitution of formula (16) to:
wherein,respectively equal value new energy unit inertia time constant H ne Minimum and maximum of (2); />Respectively equal value new energy unit primary frequency modulation gain K ne Minimum and maximum of (2); />The system frequency deviation value of the nth step under the low-frequency disturbance is equal to the inertia time constant H of the new energy unit ne Is a product of (2); />The system frequency deviation value of the nth step under low-frequency disturbance and the inertia time constant K of the equivalent new energy unit ne Is a product of (2); />The maximum deviation value limit value of the system frequency under low-frequency disturbance is set;
for high frequency disturbances, the following linear constraints are added: :
and the equivalent substitution of formula (22) to:
wherein,the system frequency deviation value of the nth step under high-frequency disturbance and the inertia time constant H of the equivalent new energy unit ne Is a product of (2); />The system frequency deviation value of the nth step under high-frequency disturbance and the inertia time constant K of the equivalent new energy unit ne Is a product of (2); />The maximum deviation value limit value of the system frequency under high-frequency disturbance is set;
in order to ensure the stable frequency of the high-proportion new energy power system, the maximum deviation value of the frequency of the high-proportion new energy power system is required to be not more than a required given value, namely:
Wherein,the system frequency deviation values of the nth step length under the low-frequency disturbance and the high-frequency disturbance are respectively;the maximum deviation value limit value of the system frequency under the low-frequency disturbance and the high-frequency disturbance is respectively set.
5. The method for calculating the frequency modulation parameter adjustable range decoupling of the new energy power system according to claim 4, wherein in step S4, since the frequency modulation process dynamic equations of the time domain discretization are all linear constraints, a frequency modulation parameter safety domain convex set is constructed; calculating a frequency modulation parameter safety domain through a PVE algorithm, firstly solving vertexes of the overall shape of the frequency modulation parameter safety domain, then expanding the existing vertex set, and calculating new vertexes beyond the current approximation value; the PVE algorithm objective function and constraints are as follows:
wherein α is a two-dimensional vector representing the direction of the identified vertex; h ne Virtual inertia time constant of the new energy unit with equivalent system; k (K) ne Primary frequency modulation gain coefficient of the system equivalent new energy unit;
the specific operation is as follows: firstly, enabling alpha to be the base of coordinate axes corresponding to two frequency modulation parameters respectively, further respectively obtaining frequency modulation parameter points corresponding to the maximum value and the minimum value of the two frequency modulation parameters, and further determining the basic shape of a frequency modulation parameter security domain; then, alpha is respectively made to be the external normal vector of each side in the current safety domain approximation value, so that new vertexes outside the current vertex set are solved; let Deltah (i,k) The distance between the solved new vertex and the primary side of the safety domain approximation is calculated, wherein i is the number of circles around the safety domain approximation, and k is the number of the solved new vertex in one circle around the safety domain approximation; order D (i) ＝max{Δh (i,k) K is the maximum value of the distance between the new vertex and the primary side of the security domain approximation in one circle around the security domain approximation; if D (i) And not more than a pre-specified error margin epsilon, terminating the algorithm, and outputting the convex hull of the existing vertex as a frequency modulation parameter safety domain.
6. The method for calculating the decoupling of the adjustable range of the frequency modulation parameter of the new energy power system according to claim 5, wherein in step S5, considering the adjustable range of the frequency modulation parameter, constructing a two-dimensional frequency modulation parameter rectangular security domain with minimum frequency modulation cost, and implementing decoupling among the frequency modulation parameters, the specific operations are as follows:
(1) Examining inscribed rectangles of the security domain of the frequency modulation parameters, and arranging each of the security domains of the frequency modulation parameters in a counterclockwise directionVertices forming a vertex set v= { V i I=1.2, … N }, where V i The ith vertex is the polygon, and N is the number of polygon vertices; defining vertex vector alpha i I=1.2, … N is the vertex V i In a counter-clockwise direction to its next adjacent vertex V i+1 Wherein the vertex vector alpha N Is the vertex V N To the vertex V 1 Is a direction vector of (2);
(2) Constructing parallel clusters which are parallel to the longitudinal axis of the frequency modulation parameter safety domain and have two intersection points with the edges of the safety domain polygon, wherein the distance between adjacent parallel lines is a given value; for the ith parallel line, the two intersection points of the ith parallel line and the edge of the polygon are respectively I i,1 、I i,2 Through I i,1 、I i,2 The component signs of the vertex vectors of the frequency modulation parameter safety domain in the transverse axis direction are opposite; respectively pass through I i,1 、I i,2 Parallel lines are made in the same direction of the transverse axis of the frequency modulation parameter safety domain, and two intersection points I are respectively formed between the two parallel lines and the edges of the polygon i,4 、I i,3 Through I i,4 、I i,3 The component signs of the vertex vectors of the frequency modulation parameter safety domain in the transverse axis direction are opposite; i is as follows i,1 、I i,2 、I i,3 、I i,4 Forming inscribed rectangles of the frequency modulation parameter security domain for the vertexes;
(3) Sequentially substituting four vertexes of each inscribed rectangle in the frequency modulation parameter security domain into a Simulink model for inspection, if a certain vertex does not meet the frequency stability requirement, enabling the vertex to be compressed inwards along a connecting line of the vertex and the center of gravity of the inscribed rectangle until the frequency modulation parameter value corresponding to the vertex meets the frequency stability constraint condition, and adjusting coordinates of two adjacent vertexes according to the updated vertex to form a decoupling rectangle meeting the frequency stability constraint;
(4) Considering that the frequency modulation cost corresponding to the frequency modulation parameter is minimum, and measuring the average frequency modulation cost corresponding to the current frequency modulation parameter adjustable range by means of the average frequency modulation cost corresponding to the four vertexes of the decoupling rectangle in the frequency modulation parameter safety domain.
CN202311654824.6A 2023-12-05 2023-12-05 Calculation method for decoupling frequency modulation parameter adjustable range of new energy power system Pending CN117638990A (en)

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