CN113746114B - Control method and system for optimizing frequency modulation of island power grid - Google Patents

Control method and system for optimizing frequency modulation of island power grid Download PDF

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CN113746114B
CN113746114B CN202111026804.5A CN202111026804A CN113746114B CN 113746114 B CN113746114 B CN 113746114B CN 202111026804 A CN202111026804 A CN 202111026804A CN 113746114 B CN113746114 B CN 113746114B
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frequency modulation
power grid
power
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CN113746114A (en
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徐思佳
尹雪梅
王小芬
燕小芬
杨华
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PowerChina Jiangxi Electric Power Engineering Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

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  • Nonlinear Science (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention discloses a control method and a system for frequency modulation of an island power grid, wherein the method comprises the following steps: a flexible electric load balancing device is connected to a load end loop, and a load end frequency modulation model is established; and establishing a generator end frequency modulation model at a generator end, monitoring the real-time operation condition of the island power grid, and starting the load end frequency modulation and generator end frequency modulation model when the island power grid suddenly throws a large load and/or before preparing to increase a large-capacity load, so as to jointly realize the control of the frequency of the power grid system. According to the invention, through the frequency modulation model of the cooperative output of the load end and the generator end, the system frequency fluctuation is smaller, and the stable frequency is closer to the rated frequency; when the system is connected with a large load, the electric load balancing device is put into the system in advance, so that the condition that the frequency of the system drops in a cliff-type manner can be avoided, the frequency dropping process is split, the pressure of equipment in the system is relieved, and a certain guarantee is provided for the frequency regulation of an island power grid.

Description

Control method and system for optimizing frequency modulation of island power grid
Technical Field
The invention belongs to the field of power grid frequency modulation, and particularly relates to a control method and a control system for optimizing frequency modulation of an island power grid.
Background
The island operation is a special and real power grid operation mode, has the characteristics of small scale and poor self-balancing capability, any load disturbance can bring larger fluctuation to the island power grid frequency and even cause power grid breakdown, and the maintenance of the frequency stability has great significance for ensuring the long-term stable operation of the island power grid.
In an island power grid, a primary frequency modulation is generally adopted to adjust the frequency of a power grid system, and a difference adjustment coefficient, a frequency modulation dead zone and OPC (Over speed protected Controller) fixed value setting are main factors influencing the frequency modulation capability of the primary system. The primary frequency modulation is combined with the secondary frequency modulation, the frequency of the power system can be adjusted in a non-differential mode, the power grid system can be adjusted in a uniform, secondary and tertiary mode through ultra-short-term load prediction to be configured in a time sequence, and the island frequency can be controlled in a targeted mode.
The current frequency modulation is mainly carried out at a motor end, but when a large load suddenly thrown or suddenly accessed in a power grid system, although the frequency modulation at the generator end can stabilize the frequency, certain fluctuation and disturbance still exist at the early stage of the frequency modulation, a Flexible Electric Load Balancing Device (FELBD) with stable frequency modulation capability is incorporated into the load end in an island power grid system to balance supply and demand power, how to establish a load end frequency modulation model to realize quick adjustment of frequency in a very short time, realize the no-difference control of the frequency of the power grid system under the condition of sudden throwing of the large load, and solve the technical problem urgently at present.
Disclosure of Invention
The invention provides a control method for frequency modulation by considering cooperative output of a load end and a generator end on the premise that an island power grid has small capacity and poor frequency and voltage stability.
According to the method, a frequency modulation model considering cooperative output of a load end and a generator end is established by using a flexible electric load balancing device based on a thyristor, time is strived for frequency modulation of the generator end according to the characteristic that the output of the electric load balancing device is rapid, and the precision of the frequency modulation model is adjusted according to the characteristic that the output of the generator end is high in precision.
The invention discloses a control method based on island power grid frequency modulation, which comprises the following steps:
a flexible electric load balancing device is connected to a load end loop, and a load end frequency modulation model is established;
establishing a generator end frequency modulation model at a generator end;
and monitoring the real-time operation condition of the island power grid, and starting the load end frequency modulation model and the generator end frequency modulation model when the island power grid suddenly throws a large load and/or before preparing to access a large-capacity load, so as to jointly realize the frequency control of the power grid system.
Most of equipment in modern social production has corresponding frequency characteristics, and the large-amplitude fluctuation of the frequency of a power grid system influences the work of electronic equipment and even damages the equipment. Frequency deviation of power grid system is
Figure BDA0003243836060000021
Wherein f is N For rating the frequency, f, of the grid system O For the real-time frequency, K, of the grid system D And regulating power for a unit of the power grid system, wherein delta P is power deviation of the power grid system.
The power deviation Δ P of the power grid system is determined by the total output power of the generator end and the total required power of the load end, so that the following steps are provided:
ΔP＝P G -P L ＝P LR -P L
wherein P is G Total output power at generator end, P LR For the actual total power consumption of the load side, P L The total required power of the load end.
The total output power of the generator and the total power demand of the load end can be obtained by the output power of each motor and the power demand of each load
Figure BDA0003243836060000031
Figure BDA0003243836060000032
Wherein P is Gi For the output power of the ith generator, a total of J loads, P, in the grid system Lj The demanded power of the jth load.
The invention is characterized in that a flexible electric load balancing device (FELBD for short) is connected to the load end, the switching response speed is high, the time sequence is good, the reliability is high, the control is easy, the frequency can be adjusted by adding the FELBD, thereby eliminating the power deviation of a power grid system and further solving the problem that the frequency modulation capability at the generator end is limited. Since the island grid system is relatively small, it is possible to change the power demand of the load end, and it mainly depends on the FELBD to absorb the excess power in the grid system.
The FELBD investment strives for time for frequency tuning, but due to its sharpness constraints, no more precise frequency tuning can be achieved. In order to realize accurate and rapid frequency modulation of a power grid system, frequency modulation at a generator end needs to be matched with frequency modulation of a FELBD. The frequency modulation at the generator end mainly realizes frequency adjustment through a steam turbine speed regulating system, an excitation system and a static stabilizer of a power system.
In a second aspect of the present invention, there is also provided a control system for frequency modulation of an islanded power grid, including:
the monitoring module is used for monitoring the real-time operation condition of the island power grid;
the frequency modulation model establishing module is used for accessing the flexible electric load balancing device in a load end loop, establishing a load end frequency modulation model and establishing a generator end frequency modulation model at a generator end;
the monitoring module is used for monitoring the real-time operation condition of the island power grid;
the load end frequency modulation module is used for starting the flexible electric load balancing device to work when the island power grid suddenly throws a large load and/or before a large-capacity load is prepared to be added;
and the generator end frequency modulation module is used for starting a generator end frequency modulation model and is matched with the load end frequency modulation model to jointly realize frequency control on the power grid system.
Compared with the prior art, the control method and the control system based on the frequency modulation of the island power grid disclosed by the invention achieve the following technical effects:
1. the FELBD is put into the power grid system according to the echelon before the power grid system is connected with the large load, so that the condition that the frequency of the power grid system falls down in a cliff-type mode can be avoided, the pressure of frequency fluctuation on equipment in the power grid system is reduced, and the advance scheduling before the large load is connected into the power grid system is important for keeping the frequency of the power grid system stable.
2. The FELBD is put into the power grid system under the condition that the large load is suddenly thrown, so that the frequency can be quickly recovered and stabilized, and the frequency fluctuation caused by the unbalance of the system power supply and demand is greatly reduced.
3. Under the condition of suddenly throwing large load, the fed FELBD is reasonably matched, and the frequency of the power grid system can be adjusted without difference.
Drawings
FIG. 1 is a diagram of a FELBD circuit model in the present invention;
FIG. 2 is a current-voltage diagram of a FELBD in the present invention;
FIG. 3 is a graph of FELBD firing angle and active and reactive power in the present invention;
FIG. 4 is a graph of load change under a sudden high load rejection in an embodiment of the present invention;
FIG. 5 is a graph of load change under start-up load in an embodiment of the present invention;
FIG. 6 is a diagram of a system frequency control model in an embodiment of the present invention;
FIG. 7 is a diagram of a turbine governor control model in an embodiment of the present invention;
FIG. 8 is a diagram of an excitation system control model in an embodiment of the invention;
FIG. 9 is a diagram of a static stabilizer control model in an embodiment of the present invention;
FIG. 10 is a graph of frequency of a large load thrown before and after a power component is introduced in an embodiment of the invention;
FIG. 11 is a graph of a frequency curve for a no-difference adjustment in an embodiment of the present invention;
fig. 12 is a frequency graph of a large load before and after the introduction of a power component in an embodiment of the present invention.
Detailed Description
The control method and the control system in the embodiment of the invention are mainly applied to an island power grid, the capacity is small, the frequency and voltage stability is poor, any load disturbance can bring large fluctuation to the frequency of the island power grid and even cause power grid collapse, the frequency modulation of the island power grid is optimized by using the flexible electric load balancing device based on the thyristor, time is won for frequency modulation at a generator end according to the characteristic that the output of the electric load balancing device is quick, and the precision of a frequency modulation model is adjusted by the characteristic that the output of the generator end is high in precision. The ETAP simulation platform is used for carrying out simulation analysis on a certain industrial park power grid system, and the fact that when the power grid system suddenly throws a large load, the frequency fluctuation of the power grid system can be smaller and the stable frequency is closer to the rated frequency through the frequency modulation model of the cooperative output of the load end and the generator end relative to the independent frequency modulation model of the generator; the size of the electric load balancing device is reasonably set, and the frequency can be adjusted without difference under the working condition. When the power grid system is connected with a large load, the electric load balancing device is put into the power grid system in advance, so that the situation that the frequency of the power grid system falls down in a cliff-breaking mode can be avoided, the frequency falling process is split, and the pressure of equipment in the power grid system is relieved.
The control method based on the frequency modulation of the island power grid disclosed by the embodiment comprises the following steps:
1. a flexible electric load balancing device (hereinafter referred to as FELBD) is accessed to a load end loop, and a load end frequency modulation model is established and accessed;
the FELBD is formed by connecting a thyristor switch and a nichrome metal resistor in series, and the resistor consumes redundant active power of a power grid system. However, the resistance value of the resistor increases when the temperature of the resistor rises after the resistor is heated, and the resistance power decreases under the condition that the voltage is not changed. The temperature coefficient of the resistor is different according to different nickel chromium content, and the resistance value in the hot state is 1.05-1.6 times of that in the cold state. The problem of resistance value change can be well solved by adopting the thyristor switch for adjustment. In addition, the thyristor has the advantages of smooth adjustment, high corresponding speed, unlimited adjustment times, phase-separable adjustment and the like. An equivalent single-phase circuit model of the device is shown in fig. 1, and a circuit is formed by connecting two thyristors and a metal resistor in series. The resistance value can change along with the temperature change, so that the influence of resistance value change is brought, and the thyristor has an adjusting function and can well solve the problem.
The device changes the voltage and the current on the power element by changing the conduction angle of the power electronic element thyristor in each period, thereby changing the overall power output, as shown in figures 2 and 3. Fig. 2 shows a graph of the voltage at the external end of the thyristor and the current through the device as a function of the conduction angle, and fig. 3 is a graph of the firing angle and active and reactive power of the device.
After the load end frequency modulation model is accessed, the FELBD has the characteristics of high switching response speed, good time sequence, high reliability and easy control, and the frequency can be adjusted by adding the FELBD, so that the power deviation of a power grid system is eliminated, and the problem that the frequency modulation capability of a generator end is limited is solved. Since the island grid system is relatively small, it is possible to change the power demand of the load end, and it mainly depends on the FELBD to absorb the excess power in the grid system.
2. And establishing a generator end frequency modulation model after the FELBD is accessed. The frequency modulation at the generator end is mainly realized by the matching of a turbine speed regulating system, an excitation system and a static stabilizer of a power grid system.
3. And monitoring the real-time operation condition of the island power grid, starting the load end frequency modulation model when the island power grid suddenly throws a large load, and/or starting the load end frequency modulation before preparing to increase a large-capacity load, and realizing the control of the power grid system frequency by cooperating with the generator end frequency modulation model.
The FELBD investment strives for time for frequency tuning, but due to its sharpness constraints, no more precise frequency tuning can be achieved. In order to realize accurate and rapid frequency modulation of a power grid system, frequency modulation at a generator end needs to be matched with frequency modulation of a FELBD.
The FELBD investment strives for time for frequency tuning, but due to its sharpness constraints, no more precise frequency tuning can be achieved. In order to realize accurate and rapid frequency modulation of a power grid system, frequency modulation at the generator end needs to be matched with frequency modulation of the FELBD.
And simulating the two working conditions of sudden load shedding and load increasing by using an ETAP simulation platform. In order to avoid long-time large-amplitude disturbance of the frequency of the power grid system, the invention adopts a frequency control model considering the load end and the generator end at the same time. The load end utilizes a 60WM power adjusting module with 6 loops to quickly adjust the frequency of a power grid system, each loop comprises a 10MW power component, and the FELBD adopts a thyristor-based flexible load balancing device with the resolution of 0.1 MW; the turbine speed regulator, the IEEET3 excitation system and the static stabilizer of the IEEET1 power system are adopted at the engine end to accurately regulate the system frequency, wherein the droop control method is adopted in the turbine speed regulation model. And putting the FELBD in advance according to the echelon before the power grid system is connected with the large load, putting the FELBD under the condition that the power grid system suddenly throws the large load, and analyzing and comparing the frequency change of the power grid system which is not connected with the FELBD.
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.
1. Establishing frequency modulation model for accessing FELBD load end
The method considers two conditions of sudden large load shedding and large load starting which can occur in an island power grid.
1) Island power grid sudden-throwing large load
As shown in fig. 4, before 50s, the grid system is in a stable state, and at this time, the total output power at the generator end of the grid system, the actual total consumed power at the load end, and the total required power at the load end are equal to each other. When the load is suddenly thrown away at 50s, the total required power of the load end is suddenly reduced, and at the moment, the total output power is larger than the total required power, so that the frequency of the power grid is increased. In order to prevent the impact from causing huge loss on the generator and the production equipment, the FELBD is added, the monitoring power grid system detects that the load suddenly drops and the FELBD with the corresponding capacity is put into the monitoring power grid system to maintain the balance of output power and required power, and time is strived for frequency modulation of the generator set, as shown by a curve between 50s and 60 s. When the load to be thrown away no longer needs to be started within a short time, the islanded grid will sequentially cut off the FELBD between 60s and 80s in time sequence.
After the FELBD is added, due to the sudden load shedding of the downstream, the FELBD is considered to be put into operation and needs to be completed in a very short time, so that the FELBD is considered to be instantaneous, and the total required power of a load end is
P L2 ＝P L1 +k * P LB
Figure BDA0003243836060000081
s.t.0≤k * ≤K
0≤-K S Δf lim ≤ΔP
Wherein P is L1 For introducing the total required power of the load end before the FELBD, wherein P L2 For introducing total required power of load end after FELBD, P LB For a single FELBD load in a load balancing system (also referred to as the resolution of the FELBD), k * For an electrical loadThe balance system needs to input the number of equipment, and floor () is a rounding-down function. When the frequency deviation of the power grid system is higher than the allowable frequency forward fluctuation upper limit delta f of the power grid system lim In time, the grid system quickly puts FELBDs to fill up defective loads and maintain the balance of the grid system, and the grid system is assumed to have K FELBDs, and the load of each device is P LB The flexible electric load balancing device can fill KP at most LB The load of (2).
If the grid system does not need to restart the load within a short time, the FELBD can be cut off gradually along with the time, and the assumption is that the load is not restarted at T EB At the moment, the power grid system already starts to cut off the load, and the required power of the load end at the moment T is as follows:
Figure BDA0003243836060000082
Figure BDA0003243836060000083
k E (t)P LB ≤(1-β)ΔP lim
wherein k is E (t) is the number of devices removed from the power grid system in the t unit time, delta P lim And (4) considering that a certain margin is reserved for the maximum output increased by the generator set per unit time, and adding a residual output margin beta of the generator set.
FELBD fastest ablation time is
Figure BDA0003243836060000091
And the ceiling () is an upward rounding function, and under the condition of fastest cutting, the output margin of the generator set is not reserved or only a minimum margin is reserved.
2) Island power grid start heavy load
As shown in fig. 5, when 50s, a downstream high-capacity electrical load is ready to start, at first, the FELBD is gradually put in 30s, so that the frequency modulation capacity of the generator set is slowly increased between 30s and 50s, the output of the generator is increased, and therefore the purpose of increasing the output in advance is achieved, and once the load sudden increase of a line to be accessed is monitored and detected, the FELBD with the corresponding capacity is cut off, so that the output power and the required power are kept in dynamic balance. The time period device ablation is shown by the FELBD demand power curve between 50s and 55 s.
Suppose at T PB The moment starting power balance system is put into the FELBD according to the power requirement of the high-capacity equipment to be accessed, and the total required power of the load end at the T moment is
Figure BDA0003243836060000092
Figure BDA0003243836060000093
k P (t)P LB ≤(1-β)ΔP lim
Wherein k is P (t) the number of FELBDs put into the electric load balancing device in the t-th unit time.
If the power grid system needs to be connected with a large-capacity device, the minimum reserved time T should be advanced Pmin And informing a power grid system to ensure that the FELBD is successfully put into operation. The minimum reserved time can be obtained by the following formula
Figure BDA0003243836060000101
/>
Wherein P is EXP For the capacity increase of the planned starting equipment, under the condition of minimum reserved time investment, the output margin of the generator set is not reserved or only a minimum margin is reserved.
Grid system at T PF FELBD putting into operation within a period of time T PF At a moment have
Figure BDA0003243836060000102
Grid system slave T PF The start-up of the large-capacity device is started,the power grid system needs to cut off the FELBD according to the increased load of the system, and the cutting rule is as follows
Figure BDA0003243836060000103
Figure BDA0003243836060000104
Wherein Δ P EXP (t) is the load that the actual load increases during the tth time. And establishing a generator-end frequency modulation model.
The frequency modulation of the generator is mainly realized by a turbine speed regulating system, an excitation system and a static stabilizer of a power system together.
The system frequency control model is shown in fig. 6, and controls the rotation speed of the turbine according to the information of the system output frequency change, and eliminates the deviation by comparing the deviation between the system output frequency and the expected quantity to obtain the expected system performance. In the control system, a signal forward path from an input end to an output end and a signal feedback path from the output end to the input end are both arranged, and the signal forward path and the signal feedback path form a closed negative feedback loop, so that the aim of keeping the output quantity consistent with the expected value in operation is fulfilled. Where Δ E is the frequency deviation integral controller increment, Δ P m For generator output power increment, Δ P D For the power increment required by the load, Δ P V For adjusting valve position increment, Δ P B For power component output power increment, Δ F 1 For frequency-modulated control signals of power component systems, Δ P ref.b For frequency-modulated control signals of generators, Δ P ref.s For integral control of gain, K E For speed regulation coefficient of speed regulator, R is system inertia constant, M is load damping coefficient, D is low-pass filter time constant, T LPF As generator time constant, Δ F 0 For system frequency adjustment, S is Laplace operator, T t Is a time constant.
The control principle of the turbine governor system is shown in FIG. 7, where W and W ref Individual steam turbine rotorSpeed and set rated speed, F hp For total capacity of the front shaft of the reheater, T C For controlling the time constant of the amplifier, T ch And T rh Respectively steam box time constant and reheater time constant, T sr Is the speed relay time constant.
Transfer function of steam turbine governor can be found from FIG. 7
Figure BDA0003243836060000111
The excitation system control principle is shown in FIG. 8, where V RMAX Is the maximum excitation voltage E fdMAX Excitation function value of, K A For regulator gain, K E As excitation constant of the field of excitation, K F To stabilize the voltage gain, K I Is a current loop gain factor, K P Is a potential circuit gain coefficient, T A To stabilize the time constant of the amplifier, T E As excitation time constant, T F Is the second time constant of the voltage regulator, T R For the regulator input filter time constant, I fd For synchronous machine excitation current, E fd In order to excite the output voltage of the synchronous machine,
Figure BDA0003243836060000112
respectively, generator terminal voltage and current, V thev For point location circuit output voltage, V ref Is a voltage regulator reference voltage, V RMIN For the minimum output voltage of the regulator, V BMIN Is the minimum power of the regulator. The frequency filter time constant a can be derived ∑ by>
Figure BDA0003243836060000113
Wherein X L Is a potential source reactance.
The transfer function of the excitation system can be determined from fig. 8
Figure BDA0003243836060000114
The static stabilizer of the power grid system is used as an additional device of an excitation system, and has the function of inhibiting active oscillation, and the control principle is shown in fig. 9.
The generator speed, the generator terminal voltage and the grid system frequency can be used as the input of a system static stabilizer, wherein K S For systematic static stabilizer yield, A 1 And A 2 Is the time constant of the frequency filter, T 3 And T 4 To compensate for time constant, T, in advance 2 And T 1 Compensating the time constant for hysteresis, T 5 For the time constant of flushing, T 6 Is the sensor time constant.
The transfer function of the static stabilizer of the system can be determined from FIG. 9
Figure BDA0003243836060000121
2. Example analysis on ETAP platform by using certain industrial park data
An industrial park in Sula Venice Indonesia is positioned on a Sula Venice island, and the load is completely powered by a 150MW unit on the island, and the island belongs to typical isolated network operation. The 150MW power grid unit is connected with a 110KV bus at a power supply end through a step-up transformer, and is connected with a 0.485KV bus through a double-circuit connecting line through a 110KW bus at a load end through a step-down transformer to supply power to a 48MW load. The load comprises various time-varying nonlinear devices including an electric furnace, the electrode action and the slag discharge of the electric furnace can cause the power fluctuation of a power grid system to be large, the collapse and the electrode burnout can further reduce part of the load to zero within a certain time, and the impact is caused to the power grid system. The simulation equivalent model of the electric furnace equipment is as follows:
R(t)＝C*L*e^(1/(A+B[1-cos(2wt+D+θ)]))
wherein omega =2 pi f, f is the frequency of a power grid system 50Hz, theta is a current hysteresis voltage phase angle, the power factor is cos theta =0.92, D is an arc thermal inertia influence factor, A = T0/a, B = (T1-T0)/2a, T0 is the minimum temperature of an arc and 1250 ℃, T1 is the maximum temperature of the arc and 1500 ℃, L is the arc length of the arc, the average value is 2 meters, and C is a load factor.
In order to avoid long-time large-amplitude disturbance of the frequency of the power grid system, a frequency control model considering the load end and the generator end simultaneously is adopted in the park. The load end utilizes a 60WM power adjusting module with 6 loops to quickly adjust the frequency of a power grid system, each loop comprises a 10MW power component, and the FELBD adopts a thyristor-based flexible load balancing system with the resolution of 0.1 MW; the turbine speed regulator, the IEEET3 excitation system and the static stabilizer of the IEEET1 power system are adopted at the machine end to accurately adjust the frequency of the power grid system, wherein the speed regulation model of the turbine adopts a droop control method, the static stabilizer of the power system takes the angular rotation speed of a motor as input, and the parameters of the turbine speed regulator, the excitation system and the static stabilizer of the power system are shown in tables 1-3:
TABLE 1 steam turbine governor parameter table
Figure BDA0003243836060000131
TABLE 2 excitation system parameter table
Figure BDA0003243836060000132
TABLE 3 electric power system stabilizer parameter table
Figure BDA0003243836060000133
An ETAP simulation platform is used for simulating two working conditions of sudden heavy load shedding and load increasing, and FIG. 10 shows the frequency change condition of the power grid system when the parameters are adopted and the large load is suddenly shed. As can be seen from fig. 10, when t =1s, a 48MW load line of one circuit suddenly throws a large load, the power of the load end is greatly reduced in a short time, which causes imbalance in the power supply and demand of the power grid system, the power generated at the machine end is greater than the actual power demand of the load, which causes a rapid increase in the frequency of the power grid system, and the speed regulation system immediately starts to perform primary frequency modulation on the power grid system. The speed regulating system can only carry out differential regulation, so that the frequency of the power grid system is finally stabilized at about 50.2Hz, and the frequency fluctuation reaches over 0.2Hz in the period of 0 to 5 seconds. When the FELBD is put into operation, the frequency of the grid system is significantly improved, and the frequency change is shown in fig. 10. After the power grid suddenly throws a large load, the power balance condition of the system is immediately analyzed by monitoring and finding an abnormal working condition, and the frequency cannot be quickly controlled within an allowable range by only depending on a machine-end speed regulating system through calculation. 48MW FELBD was launched at time t =1.2s based on the monitored load shed value. The system frequency rapidly stabilized at 49.983Hz after a brief oscillation. As can be seen, the maximum frequency fluctuation after the frequency burst is only 0.05Hz, which is much smaller than the fluctuation when the FELBD is not applied.
The final stable position of the frequency will also change by adjusting the fed FELBD by the automatic control system, as shown in fig. 11. When 44MW is put in, the grid system frequency is substantially stabilized at 50Hz at time t =10s, which illustrates that a homodyne adjustment of the grid system frequency can be achieved in case of sudden load shedding by adding a FELBD.
Fig. 12 shows that when the above parameters are used, a 48MW load line of the grid system with one loop is connected to the grid system at the time t =51.1s, the power of the load end is greatly increased in a short time, which causes imbalance of supply and demand of the system power, and the system frequency drops in a cliff manner within 5s, and finally stabilizes at about 49.8 Hz. Such frequency fluctuations can cause damage to equipment within the system, placing tremendous pressure on motor frequency modulation. To mitigate premature injection of motor frequency modulated pressure into the FELBD, the system frequency is varied as shown in fig. 12. Monitoring that a loop 48MW load line needs to be connected to the power grid after 1 minute, judging that the action causes huge impact on the frequency of the power grid, selecting to put the power grid into FELBD in advance, starting at the time of t =1s, putting 10MW of FELBD every 10s, putting 4MW of FELBD at the time of t =41s, quitting all FELBD at the time of t =51s, and connecting the load line into the system at the time of t =51.1 s. As can be seen from fig. 12, although the system frequency is still stable at about 49.8Hz, the cliff-type sag interval is split into a plurality of parts by introducing the FELBD, and the impact of introducing a heavy-load line on the system is alleviated.
According to the invention, an adjusting function of the flexible electric load balancing device is introduced on the basis of the traditional frequency modulation models of the power generation end and the load end, and frequency response curves under two conditions are compared through simulation analysis of actual engineering, so that the following conclusion is obtained;
the FELBD is put into the system in advance according to the echelon before the system is connected with the large load, so that the condition that the frequency of the system drops in a cliff-shaped mode can be avoided, the pressure of frequency fluctuation on equipment in the system is reduced, and the advance scheduling before the large load is connected into the system is important for keeping the frequency of the system stable.
The FELBD is put into the system under the condition that the system suddenly throws large load, so that the frequency can be quickly recovered and stabilized, and the frequency fluctuation caused by the imbalance of the system power supply and demand is greatly reduced.
Under the condition of sudden load shedding, the fed FELBD is reasonably matched, and the frequency of the system can be adjusted without difference.
Another embodiment of the present invention further provides a control system for frequency modulation of an island power grid, where the system includes: the system comprises a frequency modulation model establishing module, a monitoring module, a load end frequency modulation module and a generator end frequency modulation module.
The frequency modulation model establishing module is used for accessing the flexible electric load balancing device in a load end loop, establishing a load end frequency modulation model and establishing a generator end frequency modulation model at a generator end;
the monitoring module is used for monitoring the real-time operation condition of the island power grid;
the load end frequency modulation module is used for starting the load end frequency modulation when the island power grid suddenly throws a large load and/or before preparing to increase a large-capacity load;
and the generator end frequency modulation module is used for starting the generator end frequency modulation model so as to be matched with the load end frequency modulation model. The flexible electric load balancing device is formed by connecting a thyristor switch and a nichrome metal resistor in series, and the power output of the power element is changed by changing the conduction angle of the thyristor in each period. The generator-end frequency modulation module comprises a steam turbine speed regulation system, an excitation system control system and a static stabilizer of a power grid system.
According to the embodiment of the invention, the frequency fluctuation of the system can be smaller through the frequency modulation model of the cooperative output of the load end and the generator end, and the stable frequency is closer to the rated frequency; the size of the electric load balancing device is reasonably set, and the frequency can be adjusted without difference under the working condition. When the system is connected with a large load, the electric load balancing device is put into use in advance, so that the condition that the frequency of the system drops in a cliff-type manner can be avoided, the frequency dropping process is split, the pressure of equipment in the system is relieved, and a certain reference is provided for the frequency regulation of the island power grid.
The foregoing description shows and describes several preferred embodiments of the invention, but as aforementioned, it is to be understood that the invention is not limited to the forms disclosed herein, but is not to be construed as excluding other embodiments and is capable of use in various other combinations, modifications, and environments and is capable of changes within the scope of the inventive concept as expressed herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (8)

1. A control method for frequency modulation of an island power grid is applied to an island power grid operation mode, and is characterized by comprising the following steps:
a flexible electric load balancing device is connected to a load end loop, and a load end frequency modulation model is established;
establishing a generator end frequency modulation model at a generator end;
monitoring the real-time operation condition of an island power grid, starting the load end frequency modulation model and the generator end frequency modulation model when the island power grid suddenly throws a large load and/or before preparing to access a large-capacity load, and realizing the frequency control of a power grid system together, wherein the method specifically comprises the following steps:
before increasing a large-capacity load, the power grid system is gradually accessed into the flexible electric load balancing device according to the echelon within the reserved time, and meanwhile, the flexible electric load balancing device with the corresponding capacity is cut off when the load of a line to be accessed is monitored to be suddenly increased, so that the power and the output power of a demand end are dynamically balanced;
if the power grid system is to be connected to the high-capacity load equipment, the power grid system is informed of the reserved time in advance, wherein the reserved time is the minimum reserved time and is obtained by the following calculation formula:
Figure FDA0003943441720000011
wherein, T pmin Denotes the minimum reservation time, P EXP Increased capacity, Δ P, for planned starting of the plant lim The maximum output is increased for the unit time of the generator set, and under the condition of minimum reserved time investment, the output margin of the generator set is not reserved or only a minimum margin is reserved;
grid system at T PF Completing the operation of the flexible electric load balancing device at time interval T PF At a moment have
Figure FDA0003943441720000012
Wherein, P L Is shown at T PF Total power demand, P, at the moment of time L1 Is the required power of the 1 st load, P EXP Increased capacity for planned starting of the plant, K p (T) is the potential circuit gain coefficient in the T-th time period, T PB FELBD time, T, for a power balancing system PF Time to turn on a large capacity device, P LB Representing the load of a single FELBD in a load balancing system, the grid system from T PF Starting high-capacity equipment, and cutting off the flexible electric load balancing device according to the increased load of the power grid system according to the following cutting rule:
Figure FDA0003943441720000021
Figure FDA0003943441720000022
wherein, K E (t) is the excitation constant of the excitation field during the t-th time period, Δ P EXP (t) the load to which the actual load increases during the t-th time period, P LB Representing the load of a single FELBD in a load balancing system, K p (T) the number of FELBDs put into the electric load balancing device in the tth unit time, T PB FELBD time, T, for a power balancing system PF Time to turn on the mass storage device.
2. A method for controlling frequency modulation in an islanded grid according to claim 1, wherein the flexible electrical load balancing means comprises a thyristor switch and a nichrome metal resistor connected in series, and the power output of the power element is varied by varying the conduction angle of the thyristor in each cycle.
3. The island power grid frequency modulation control method according to claim 1, wherein the generator-side frequency modulation model mainly realizes frequency modulation through a turbine speed regulation system, an excitation system and a static stabilizer of a power system.
4. The method for controlling frequency modulation of an islanded grid according to claim 2, further comprising:
after the load end frequency modulation model is started, when the thrown load no longer needs to be started in a short time, the power grid system sequentially cuts off the accessed flexible electric load balancing devices according to a time sequence within a preset period of time.
5. A control method for frequency modulation of an islanded grid according to claim 3, characterised in that generator speed, generator terminal voltage and grid system frequency are all used as inputs to a static stabilizer, where K is S For static stabilizer yield, A 1 And A 2 Is the time constant of the frequency filter, T 3 And T 4 To make a leadCompensating time constant, T 2 And T 1 Compensating the time constant for hysteresis, T 5 For the time constant of flushing, T 6 Is the sensor time constant, V S1 Calculating the transfer function of the static stabilizer of the system for the input of the power system stabilizer to obtain:
Figure FDA0003943441720000031
6. a control system for frequency modulation of an island power grid is characterized by comprising:
the frequency modulation model establishing module is used for accessing the flexible electric load balancing device in a load end loop, establishing a load end frequency modulation model and establishing a generator end frequency modulation model at a generator end;
the monitoring module is used for monitoring the real-time operation condition of the island power grid;
the load end frequency modulation module is used for starting the load end frequency modulation model when the island power grid suddenly throws a large load and/or before preparing to increase a large-capacity load;
the generator end frequency modulation module is used for starting a generator end frequency modulation model and is matched with the load end frequency modulation model to jointly realize frequency control on the power grid system, and the generator end frequency modulation module specifically comprises:
before increasing a large-capacity load, the power grid system is gradually accessed into the flexible electric load balancing device according to the echelon within the reserved time, and meanwhile, the flexible electric load balancing device with the corresponding capacity is cut off when the load of a line to be accessed is monitored to be suddenly increased, so that the power and the output power of a demand end are dynamically balanced;
if the power grid system is to be connected to the high-capacity load equipment, the power grid system is informed of the reserved time in advance, wherein the reserved time is the minimum reserved time and is obtained by the following calculation formula:
Figure FDA0003943441720000032
wherein, T pmin Denotes the minimum reservation time, P EXP Increased capacity, Δ P, for planned starting of the plant lim The maximum output is increased for the unit time of the generator set, and under the condition of minimum reserved time input, the output margin of the generator set is not reserved or only a minimum margin is reserved;
grid system at T PF Completing the operation of the flexible electric load balancing device at time interval T PF At a moment have
Figure FDA0003943441720000041
Wherein, P L Is shown at T PF Total power demand, P, at the moment of time L1 Is the required power of the 1 st load, P EXP Increased capacity for planned starting of the plant, K p (T) is the potential circuit gain coefficient in the T-th time period, T PB FELBD time, T, for a power balancing system PF Time to turn on a large capacity device, P LB Representing the load of a single FELBD in a load balancing system, the grid system from T PF Starting high-capacity equipment, and cutting off the flexible electric load balancing device according to the increased load of the power grid system according to the following cutting rule:
Figure FDA0003943441720000042
Figure FDA0003943441720000043
wherein, K E (t) is the excitation constant of the excitation field during the t-th time period, Δ P EXP (t) the load to which the actual load increases during the t-th time period, P LB Representing the load of a single FELBD in a load balancing system, K p (T) the number of FELBDs charged to the electric load balancing device in the tth unit time, T PB To balance the powerTime of system injection into FELBD, T PF The time to turn on the mass storage device.
7. The control system of claim 6, wherein the generator-side frequency modulation module comprises a turbine governor system, an excitation system control system and a static stabilizer of an electric power system.
8. The control system of claim 7, wherein said compliant electrical load balancing device comprises a series connection of a thyristor switch and a nichrome metal resistor, said thyristor having a conduction angle per cycle that is varied to vary the power output of the power element.
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