CN113991642A - Black start modeling method considering single power supply to drive multiple auxiliary machines - Google Patents
Black start modeling method considering single power supply to drive multiple auxiliary machines Download PDFInfo
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Abstract
The invention relates to the field of safe operation of a power system, in particular to a black start modeling method considering that a single power supply drives various auxiliary machines. The method is based on the existing bus overvoltage problem of black start modeling simulation analysis, and by modeling various main auxiliary machines of the thermal power plant, the simulation analysis of the power grid recovery process that the black start power supply in the black start scheme is started and drives the adjacent power plant to start after having power supply capacity is added, so that the potential risk excavation of the whole process of the black start scheme is realized, and the comprehensiveness, accuracy and reference value of the black start simulation modeling are greatly improved.
Description
Technical Field
The invention relates to the field of safe operation of a power system, in particular to a black start modeling method considering that a single power supply drives multiple auxiliary machines.
Background
The blackout is a serious threat to the power system all the time, the influence caused by the blackout accident is more and more serious along with the increasing scale of the power system, the high-proportion access of intermittent new energy and the continuous improvement of the dependence degree of the society on power supply, and the black start is one of important measures for the safety defense of the blackout accident, and has important significance for reducing the load recovery burden, accelerating the recovery speed of the power system and reducing the bad influence caused by the blackout accident.
The black start process is an abnormal special operation mode of the power grid operation, and under the condition that the power system loses power in a large range, the selected self-starting unit maintains the stability of voltage and frequency and drives other units without self-starting capability to recover power supply. The whole process is divided into three stages, namely a black start stage, a network reconstruction stage and a load recovery stage, after the black start stage is successful, the next step is to transmit power to a nearby power plant starting a power supply to drive an auxiliary machine of the power plant to operate, so that the power supply of the nearby power plant is started as soon as possible to form a multi-power-supply small system which is more stable than a single power supply. The black start working condition is complex, unexpected accidents and problems can occur, particularly, in the process that after the black start power supply is started and has power supply capacity, an adjacent power plant is driven to start and achieve point-area power grid recovery, simulation analysis needs to be carried out on the whole process to find potential faults in advance, and therefore countermeasures are made. However, the existing research on simulation modeling of the black start scheme of the power system only focuses on considering the overvoltage problem of an empty charging bus in the black start stage, and the electromagnetic transient simulation model of the black start path is built for the black dragon river power grid in the research on the initial overvoltage problem of power supply capacity recovery of the black dragon river power grid based on ADPSS electromagnetic transient simulation by Guoniao and Zhangxin, and the overvoltage condition of the 220kV bus in the power supply recovery process is calculated and analyzed. The literature that simulation analysis is carried out in the process of driving the auxiliary engine of the nearby power plant to start after the black start power supply is started is not found, and the actual black start test shows that the motor consumes huge power in the process of driving the auxiliary engine of the nearby power plant, so that the voltage and the frequency of the system are greatly impacted, and the evaluation of the black start result is seriously influenced.
Disclosure of Invention
In order to solve the problems, the invention provides a black start modeling method considering that a single power supply drives various auxiliary machines, the invention adds modeling research on various main auxiliary machines of a thermal power plant driven by the single power supply on the basis of the existing black start modeling, respectively establishes electromagnetic transient models of a boiler feed water pump, a condensate pump, an air feeder, an induced draft fan and a coal mill, carries out simulation calculation on the process of driving the plurality of auxiliary machines of the thermal power plant to operate after the black start is successful, brings the calculation results into the evaluation of a black start scheme, can enrich the evaluation basis of the black start test scheme, and greatly improves the accuracy and the reference value of the black start simulation modeling. The specific technical scheme is as follows:
a black start modeling method considering that a single power supply drives multiple auxiliary machines comprises the following steps:
s1: the method comprises the following steps of constructing a black-start multi-source small system model for driving various auxiliary machines by a single power supply according to a black-start scheme, wherein the black-start multi-source small system model comprises a single power supply model, a plurality of empty charging bus models and an auxiliary machine model; the single power supply model, the plurality of empty charging bus models and the auxiliary machine model are sequentially connected, wherein the auxiliary machine model comprises a boiler feed water pump, a condensate pump, a blower, an induced draft fan and an electromagnetic transient model of a coal mill;
s2: a single power supply is made to carry out sectional starting on the black-start multisource small system model, time control elements are added into each empty charging bus model and the auxiliary machine model, and the on-off time of the time control elements is set respectively and used for simulating the starting sequence of each element in the black-start multisource small system model;
s3: performing electromagnetic transient simulation calculation on the established black-start multi-source small system model with the single power supply driving various auxiliary machines, and judging whether a generator set in a simulation scheme generates self-excitation according to whether the terminal voltage and the stator current of a generator of the black-start power supply output by simulation exceed rated values;
judging whether the voltage of each empty charging bus exceeds the standard according to simulation output, and judging whether each section of no-load line in the simulation scheme generates overvoltage;
and judging whether the black-start multi-source small system model in the simulation scheme generates low-frequency oscillation or not according to the extreme voltage of the auxiliary machine and the system frequency.
Preferably, the modeling process of the condensate pump is as follows:
equation (1) can be derived from the motor differential equation:
in the formula, KaFor motor transmission coefficient, TmU (t) is the motor terminal voltage at time t,
the rotating speed of the motor rotor at the moment t;
and carrying out Laplace transform on the above formula to obtain a transfer function, and considering gear transfer between the motor and the water pump to obtain the transfer function as formula (2):
in the formula, omega(s) is the rotor speed of the generator after Laplace transformation, U(s) is the terminal voltage of the generator after Laplace transformation, and i is the gear transmission ratio; since q(s) H ═ η Ω(s), the transfer function can also be written as formula (3):
in the formula, q(s) is the outlet flow rate of the condensate pump after laplace transformation, and η is the pump transfer coefficient.
Preferably, the modeling process of the boiler feed water pump is as follows:
the power and the lift of a boiler feed water pump have a relation shown in the formula (4):
where Δ P is a variation of the power of the feed pump, H is a head of the feed pump, ρ is a density of water, g is a gravitational acceleration, and Δ P is Δ wMfTherefore, formula (5) can be obtained by laplace transformation:
in the formula, MfIs the motor moment of resistance, KfThe proportional coefficient of the resisting moment, and delta w is the variation of the rotating speed; at a nominal speed, the relationship between pump head and flow can be fitted using equation (6):
H＝α+βQ+γQ2； (6)
in the formula, Q is the flow rate of a boiler feed water pump, and alpha, beta and gamma are constant coefficients and are determined by actual pump characteristics; after linearization treatment, formula (7) is obtained:
in the formula, KeiThe proportional coefficient of the flow lift of the i-th section after the piecewise linearization, K of different sectionseiThe values are different.
Preferably, the modeling process of the air feeder and the induced draft fan is as follows:
the air feeder and the induced draft fan adjust air feeding and induced draft flow by changing the opening degree of the inlet baffle plate, so that the transfer function is the formula (4):
in the formula, λ is the efficiency of the blower or the induced draft fan, KaFor motor transmission coefficient, TmAnd (b) taking a time constant of the motor, wherein i is a gear transmission ratio, Q(s) is the outlet flow of the condensate pump after Laplace transformation, and U(s) is the voltage of the generator terminal after Laplace transformation.
Preferably, the modeling process of the coal mill is as follows:
the coal mill comprises a grinding mechanism and a coal powder separator, wherein the grinding mechanism is represented as follows by a first-order inertia link:
in the formula, Ma(s) is the amount of coal dust entering the grinding mechanism after Laplace transform, M0(s) is the amount of coal fines entering the separator after Laplace transformation, TcIs the inertia time constant of the powder process.
The coal powder separator of the coal mill is used for separating coal powder, and the dynamic process can be represented by the following formula:
M0(s)＝KbMb(s)； (10)
in the formula, Mb(s) quantity of coal dust at the outlet of the separator, KbIs the circulation coefficient of the coal dust;
in combination with the motor differential equation, the transfer function is obtained as follows:
wherein, KaFor motor transmission coefficient, TmFor the motor time constant, i is the gear ratio, and U(s) is the generator terminal voltage after Laplace transform.
Preferably, the step S1 further includes verifying accuracy of the established auxiliary model, specifically: and recording the active output of each auxiliary machine after starting, comparing the active output with the active output of each auxiliary machine actually measured on site, judging that the established auxiliary machine model is accurate if the relative error is within a set range, and if the relative error is not within the set range, reestablishing the corresponding auxiliary machine model.
Preferably, the method for setting the on-off time of the time control element in step S2 specifically includes: the on/off timings of the time control elements sequentially increase from the single power supply model to the slave model.
Preferably, the step S3 shows the transient response characteristic of the black start process in a waveform diagram manner.
The invention has the beneficial effects that: the method is used for modeling an auxiliary machine stage of a nearby power plant driven after the black start is successful, establishing a black start multi-source small system model, analyzing and evaluating a black start scheme from three main aspects of self excitation of a generator, no-load line overvoltage and low-frequency oscillation in the auxiliary machine driving process, explicitly displaying the transient response characteristic in the black start process in a oscillogram mode, and taking a simulation result as a reliable and powerful basis for judging whether the black start scheme corresponding to the model is safe or not. The method is based on the existing black-start modeling simulation analysis bus overvoltage problem, and by modeling various main auxiliary machines of the thermal power plant, the simulation analysis of the power grid recovery process that the black-start power supply in the black-start scheme is started and drives the adjacent power plant to start after having power supply capacity is added, so that the potential risk excavation of the whole process of the black-start scheme is realized, the defects of the existing modeling simulation in the analysis process and content are filled, and the comprehensiveness, accuracy and reference value of the black-start simulation modeling are greatly improved.
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In order to more clearly illustrate the detailed description of the invention or the technical solutions in the prior art, the drawings that are needed in the detailed description of the invention or the prior art will be briefly described below. Throughout the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.
FIG. 1 is a flow chart of the method of the present invention
FIG. 2 is a schematic diagram of a black-start multi-source small system model established in an embodiment of the present invention;
FIG. 3 is a diagram of a model of a condensate pump constructed in the present embodiment;
FIG. 4 is a diagram of a boiler feed water pump model built in the present embodiment;
FIG. 5 is a diagram of a model of an induced draft fan or a blower fan built in the present embodiment;
FIG. 6 is a diagram of a model of the coal pulverizer constructed in the present embodiment;
FIG. 7 is a graph comparing an active output curve of a feed pump simulation with an active output curve actually measured on site;
FIG. 8 is a graph comparing an active output curve of a condensate pump simulation with an active output curve actually measured on site;
FIG. 9 is a comparison graph of an active power output curve simulated by the induced draft fan and an active power output curve actually measured on site;
FIG. 10 is a graph comparing an active output curve of a blower simulation with an active output curve actually measured on site;
FIG. 11 is a model diagram of a black start test system of a power grid in a certain region in Guangxi;
FIG. 12 is a simulation diagram of the terminal voltage of the 1# machine of the A power plant in this embodiment;
FIG. 13 is a simulation diagram of the stator current of the 1# machine of the A power plant in the embodiment;
FIG. 14 is a simulation diagram of the voltage curve of the bus I in this embodiment;
FIG. 15 is a simulation diagram of the voltage curve of the bus bar II in the present embodiment;
FIG. 16 is a simulation diagram of the voltage curve of the bus III in this embodiment;
FIG. 17 is a simulation diagram of the terminal voltage of the auxiliary machine of the power plant B in the embodiment;
fig. 18 is a simulation diagram of the system frequency of the model in the present embodiment.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.
As shown in fig. 1, a black start modeling method considering a single power supply to drive multiple auxiliary machines includes the following steps:
s1: the method comprises the following steps of constructing a black-start multi-source small system model for driving various auxiliary machines by a single power supply according to a black-start scheme, wherein the black-start multi-source small system model comprises a single power supply model, a plurality of empty charging bus models and an auxiliary machine model; the single power supply model, the plurality of empty bus models and the auxiliary machine model are connected in sequence, wherein the auxiliary machine model comprises an electromagnetic transient model of a boiler feed water pump, a condensate pump, a blower, an induced draft fan and a coal mill. As shown in fig. 2, the power plant a is used as a single power model for black start, and the boiler feed water pump, the condensate pump, the blower, the induced draft fan, the coal mill, and the like of the power plant B are used as auxiliary machines. The power plant A serves as a black start power supply, the power plant B serves as another power supply, a black start multi-source small system model is formed and used for simulating the process that the power plant A (black start power supply) drives an auxiliary machine of the power plant B, and the auxiliary machine of the power plant B drives the power plant B to start after starting.
The modeling process of the condensate pump is as follows:
equation (1) can be derived from the motor differential equation:
in the formula, KaFor motor transmission coefficient, TmU (t) is the motor terminal voltage at time t,
the rotating speed of the motor rotor at the moment t;
and carrying out Laplace transform on the above formula to obtain a transfer function, and considering gear transfer between the motor and the water pump to obtain the transfer function as formula (2):
in the formula, omega(s) is the rotor speed of the generator after Laplace transformation, U(s) is the terminal voltage of the generator after Laplace transformation, and i is the gear transmission ratio; since q(s) H ═ η Ω(s), the transfer function can also be written as formula (3):
in the formula, q(s) is the outlet flow rate of the condensate pump after laplace transformation, and η is the pump transfer coefficient. The condensate pump model is shown in FIG. 3, where KωThe rotation speed adjustment coefficient.
The modeling process of the boiler feed pump is as follows:
the principle of the boiler feed pump is similar to that of a condensate pump, but the power and the lift of the boiler feed pump have the relationship shown in the formula (4):
wherein, Delta P is the power variation of the water feed pump, H is the delivery head of the water feed pump, rho is the density of water, g is the gravity acceleration,since Δ P ═ Δ wMfTherefore, formula (5) can be obtained by laplace transformation:
in the formula, MfIs the motor moment of resistance, KfThe proportional coefficient of the resisting moment, and delta w is the variation of the rotating speed; at a nominal speed, the relationship between pump head and flow can be fitted using equation (6): s is the frequency domain variable in the laplace transform.
H＝α+βQ+γQ2； (6)
In the formula, Q is the flow rate of a boiler feed water pump, and alpha, beta and gamma are constant coefficients and are determined by actual pump characteristics; after linearization treatment, formula (7) is obtained:
in the formula, KeiThe proportional coefficient of the flow lift of the i-th section after the piecewise linearization, K of different sectionseiThe values are different. The available boiler feedwater pump model is shown in FIG. 4.
The modeling process of the air feeder and the induced draft fan is as follows:
the air feeder and the induced draft fan adjust air feeding and induced draft flow by changing the opening degree of the inlet baffle plate, so that the transfer function is the formula (4):
in the formula, λ is the efficiency of the blower or the induced draft fan, KaFor motor transmission coefficient, TmAnd (b) taking a time constant of the motor, wherein i is a gear transmission ratio, Q(s) is the outlet flow of the condensate pump after Laplace transformation, and U(s) is the voltage of the generator terminal after Laplace transformation. The model of the blower or the induced draft fan is shown in fig. 5. T isfTime constant of air flow through the baffle, KdThe coefficient is adjusted for the fan baffle.
The modeling process of the coal mill is as follows:
the coal mill comprises a grinding mechanism and a coal powder separator, wherein the grinding mechanism is large in mass and inertia and is represented as follows by a first-order inertia link:
in the formula, Ma(s) is the amount of coal dust entering the grinding mechanism after Laplace transform, M0(s) is the amount of coal fines entering the separator after Laplace transformation, TcIs the inertia time constant of the powder process.
The coal powder separator of the coal mill is used for separating coal powder, and the dynamic process can be represented by the following formula:
M0(s)＝KbMb(s)； (10)
in the formula, Mb(s) quantity of coal dust at the outlet of the separator, KbIs the circulation coefficient of the coal dust;
in combination with the motor differential equation, the transfer function is obtained as follows:
wherein, KaFor motor transmission coefficient, TmFor the motor time constant, i is the gear ratio, and U(s) is the generator terminal voltage after Laplace transform. The coal mill model is shown in fig. 6.
Verifying the accuracy of the established auxiliary engine model, specifically: and recording the active output of each auxiliary machine after starting, comparing the active output with the active output of each auxiliary machine actually measured on site, judging that the established auxiliary machine model is accurate if the relative error is within a set range, and if the relative error is not within the set range, reestablishing the corresponding auxiliary machine model. As shown in the figures 7-10 of the drawings,
s2: and establishing a simulation scheme that a single power supply carries out sectional starting on the black-start multisource small system model, adding time control elements into each empty charging bus model and the auxiliary machine model, and respectively setting the on-off time of the time control elements for simulating the starting sequence of each element in the black-start multisource small system model. The method for setting the on-off time of the time control element specifically comprises the following steps: the on/off timings of the time control elements sequentially increase from the single power supply model to the slave model. For example, in fig. 2, the timing element addition case includes:
and step A, in a black start stage, taking the power plant A as a start power supply and putting the power load into service, carrying out isolated network operation for 5 minutes by adopting a small network automatic mode in frequency control, and setting the isolated network operation time according to the site.
And step B, in a network reconstruction stage, adding a time control element 1 into a connecting line of the transformer 1 and each section of empty charging bus in each section of bus model in the empty charging small system, setting the initial state to be disconnected, and setting the first closing time to be 80S.
And C, recovering the load, and starting the auxiliary machine of the power plant B. And adding a time control element 2 on a connecting line between each section of hollow charging bus and the transformer # 2 in the model, setting the initial state to be off, and setting the first closing time to be 150S.
S3: carrying out electromagnetic transient simulation calculation on the established black-start multisource small system model with the single power supply driving various auxiliary machines:
(1) aiming at the problem of no-load circuits, the self-excitation phenomenon of the synchronous generator refers to the phenomenon that the voltage of the generator spontaneously rises under the condition of overlarge capacitive load, and is that stator current is generated due to the magnetic assistance effect of armature reaction of the synchronous generator, and the voltage value established at the generator end rises at the moment, so that whether a generator set in a simulation scheme can generate self-excitation or not can be judged according to whether the generator end voltage and the stator current of the generator of a black start power supply output by simulation exceed a rated value or not;
(2) aiming at the problem of overvoltage of the no-load circuit, judging whether the no-load circuit of each section in the simulation scheme generates overvoltage or not according to whether the voltage of each no-load charging bus output by simulation exceeds the standard or not;
(3) aiming at the problem of low-frequency oscillation in the process of driving the auxiliary machine, whether the black start model in the simulation scheme generates low-frequency oscillation or not is judged according to the extreme voltage of the auxiliary machine and the system frequency. The transient response characteristic of the black start process is shown in a waveform diagram mode.
The whole simulation process of the black start test system of the power grid in a certain area in Guangxi is shown in FIG. 11, and the simulation test steps are as follows:
(1) simulating that a machine # 1 of an A power plant is used as a black start power supply, starting and transmitting power to a 110kV #1M bus of the A power plant, controlling the frequency of the machine # 1 of the A power plant in an automatic mode (frequency setting), gradually putting 20MW load on a 110kV side, and operating in an isolated network for 60S;
(2) simulating the 1# machine of the A power plant to switch into a manual mode (the active power is constant at 20MW), and continuing to access 15MW load at the original 20 MW; the time control element 1 is set to be in an initial state of disconnection, and the first closing time is 80S;
(3) simulating the No. 1 machine of the A power plant to enter a steady state with 35MW load;
(4) simulating an empty charging bus I; the time control element 2 sets the initial state to be off, and the first closing time is 150S;
(6) simulating an empty charging bus II; the time control element 3 sets the initial state to be off, and the first closing time is 300S;
(7) simulating an empty charging bus III; the time control element 4 sets the initial state to be off, and the first closing time is 450S;
(8) b, simulating and starting 1# auxiliary engine of the B power plant: one boiler water supply pump, one induced draft fan, one air feeder and six coal mills; the time control element 5 sets the initial state to be off, and the first closing time is 600S.
The analysis result after the simulation is as follows:
(1) the self-excitation problem of the generator in the black start stage:
the machine of the A power plant 1# is provided with an active load of 35MW and a capacitive reactive power of 10.5MVar, and the terminal voltage and the stator current of the machine of the A power plant 1# are shown in figures 12 and 13 in a black start stage. Rated parameters of the 1# machine generator of the A power plant are shown in the table 1:
TABLE 1A Power plant # 1 machine Generator parameters
| Model number | SF114-78/12830 |
| Rated power: | 114MW |
| rated stator phase voltage: | 9.09kV |
| rated stator phase current: | 2.76kA |
| power factor: | 0.875 |
| excitation voltage: | 458V |
| exciting current: | 1300A |
as can be known from the comparison of the graphs, the phase voltage and the phase current of the stator of the No. 1 machine of the A power plant are gradually stabilized after the black start stage is completed, and do not exceed the rated value, and the generator set cannot generate self-excitation in the black start test scheme.
(2) The problem of no-load line overvoltage in the network reconstruction stage is as follows:
the simulation voltage curves of the bus I, the bus II and the bus III are shown in FIGS. 14-16:
in power equipment insulation design, the overvoltage protection protocol specifies multiples of the operating voltage as shown in table 2.
TABLE 2 multiple specification of overvoltage protection protocol to operating overvoltage
| Voltage class | Multiple specification of operating overvoltages |
| 30-65kV and below system | 4.0 |
| 110-power 145kV system (non-direct grounding) | 3.5 |
| 110-220kV system (direct grounding) | 3.0 |
| 330kV system (direct grounding) | 2.8 |
| 500kV system (direct grounding) | 2.0 |
As can be seen from the comparison of the graphs, the no-load lines in each section of the black start test scheme do not generate overvoltage exceeding a specified multiple.
(3) Low frequency oscillation problem in load recovery stage:
the simulation calculation shows that after the auxiliary machine of the B power plant is merged into the system, the terminal voltage and the system frequency of the auxiliary machine of the B power plant change as shown in FIGS. 17-18, and the simulation result proves that the system frequency is stabilized at 50Hz after the load is recovered, the voltage of the auxiliary machine of the B power plant is rapidly stabilized after the auxiliary machine of the B power plant is put into operation, and the low-frequency oscillation cannot occur in the black-start test scheme.
The method is based on the existing black-start modeling simulation analysis bus overvoltage problem, and by modeling various main auxiliary machines of the thermal power plant, the simulation analysis of the power grid recovery process that the black-start power supply in the black-start scheme is started and drives the adjacent power plant to start after having power supply capacity is added, so that the potential risk excavation of the whole process of the black-start scheme is realized, the defects of the existing modeling simulation in the analysis process and content are filled, and the comprehensiveness, accuracy and reference value of the black-start simulation modeling are greatly improved.
Those of ordinary skill in the art will appreciate that the elements of the examples described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the components of the examples have been described above generally in terms of their functionality in order to clearly illustrate the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
In the embodiments provided in the present application, it should be understood that the division of the unit is only one division of logical functions, and other division manners may be used in actual implementation, for example, multiple units may be combined into one unit, one unit may be split into multiple units, or some features may be omitted.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention, and they should be construed as being included in the following claims and description.
Claims (8)
1. A black start modeling method considering that a single power supply drives multiple auxiliary machines is characterized in that: the method comprises the following steps:
s1: the method comprises the following steps of constructing a black-start multi-source small system model for driving various auxiliary machines by a single power supply according to a black-start scheme, wherein the black-start multi-source small system model comprises a single power supply model, a plurality of empty charging bus models and an auxiliary machine model; the single power supply model, the plurality of empty charging bus models and the auxiliary machine model are sequentially connected, wherein the auxiliary machine model comprises a boiler feed water pump, a condensate pump, a blower, an induced draft fan and an electromagnetic transient model of a coal mill;
s2: a single power supply is made to carry out sectional starting on the black-start multisource small system model, time control elements are added into each empty charging bus model and the auxiliary machine model, and the on-off time of the time control elements is set respectively and used for simulating the starting sequence of each element in the black-start multisource small system model;
s3: performing electromagnetic transient simulation calculation on the established black-start multi-source small system model with the single power supply driving various auxiliary machines, and judging whether a generator set in a simulation scheme generates self-excitation according to whether the terminal voltage and the stator current of a generator of the black-start power supply output by simulation exceed rated values;
judging whether the voltage of each empty charging bus exceeds the standard according to simulation output, and judging whether each section of no-load line in the simulation scheme generates overvoltage;
and judging whether the black-start multi-source small system model in the simulation scheme generates low-frequency oscillation or not according to the extreme voltage of the auxiliary machine and the system frequency.
2. The black start modeling method for driving multiple auxiliary machines by considering a single power supply according to claim 1, characterized in that: the modeling process of the condensate pump is as follows:
equation (1) can be derived from the motor differential equation:
in the formula, KaFor motor transmission coefficient, TmU (t) is the motor terminal voltage at time t,
the rotating speed of the motor rotor at the moment t;
and carrying out Laplace transform on the above formula to obtain a transfer function, and considering gear transfer between the motor and the water pump to obtain the transfer function as formula (2):
in the formula, omega(s) is the rotor speed of the generator after Laplace transformation, U(s) is the terminal voltage of the generator after Laplace transformation, and i is the gear transmission ratio; since q(s) H ═ η Ω(s), the transfer function can also be written as formula (3):
in the formula, q(s) is the outlet flow rate of the condensate pump after laplace transformation, and η is the pump transfer coefficient.
3. The black start modeling method for driving multiple auxiliary machines by considering a single power supply according to claim 1, characterized in that: the modeling process of the boiler feed pump is as follows:
the power and the lift of a boiler feed water pump have a relation shown in the formula (4):
where Δ P is a variation of the power of the feed pump, H is a head of the feed pump, ρ is a density of water, g is a gravitational acceleration, and Δ P is Δ wMfTherefore, formula (5) can be obtained by laplace transformation:
in the formula, MfFor a motor resistorMoment, KfThe proportional coefficient of the resisting moment, and delta w is the variation of the rotating speed; at a nominal speed, the relationship between pump head and flow can be fitted using equation (6):
H＝α+βQ+γQ2； (6)
in the formula, Q is the flow rate of a boiler feed water pump, and alpha, beta and gamma are constant coefficients and are determined by actual pump characteristics;
after linearization treatment, formula (7) is obtained:
in the formula, KeiThe proportional coefficient of the flow lift of the i-th section after the piecewise linearization, K of different sectionseiThe values are different.
4. The black start modeling method for driving multiple auxiliary machines by considering a single power supply according to claim 1, characterized in that: the modeling process of the air feeder and the induced draft fan is as follows:
the air feeder and the induced draft fan adjust air feeding and induced draft flow by changing the opening degree of the inlet baffle plate, so that the transfer function is the formula (4):
in the formula, λ is the efficiency of the blower or the induced draft fan, KaFor motor transmission coefficient, TmAnd (b) taking a time constant of the motor, wherein i is a gear transmission ratio, Q(s) is the outlet flow of the condensate pump after Laplace transformation, and U(s) is the voltage of the generator terminal after Laplace transformation.
5. The black start modeling method for driving multiple auxiliary machines by considering a single power supply according to claim 1, characterized in that: the modeling process of the coal mill is as follows:
the coal mill comprises a grinding mechanism and a coal powder separator, wherein the grinding mechanism is represented as follows by a first-order inertia link:
in the formula, Ma(s) is the amount of coal dust entering the grinding mechanism after Laplace transform, M0(s) is the amount of coal fines entering the separator after Laplace transformation, TcIs the inertia time constant of the powder process.
The coal powder separator of the coal mill is used for separating coal powder, and the dynamic process can be represented by the following formula:
M0(s)＝KbMb(s)； (10)
in the formula, Mb(s) quantity of coal dust at the outlet of the separator, KbIs the circulation coefficient of the coal dust;
in combination with the motor differential equation, the transfer function is obtained as follows:
wherein, KaFor motor transmission coefficient, TmFor the motor time constant, i is the gear ratio, and U(s) is the generator terminal voltage after Laplace transform.
6. The black start modeling method for driving multiple auxiliary machines by considering a single power supply according to claim 1, characterized in that: step S1 further includes verifying accuracy of the established auxiliary engine model, specifically: and recording the active output of each auxiliary machine after starting, comparing the active output with the active output of each auxiliary machine actually measured on site, judging that the established auxiliary machine model is accurate if the relative error is within a set range, and if the relative error is not within the set range, reestablishing the corresponding auxiliary machine model.
7. The black start modeling method for driving multiple auxiliary machines by considering a single power supply according to claim 1, characterized in that: the method for setting the on-off time of the time control element in step S2 specifically includes: the on/off timings of the time control elements sequentially increase from the single power supply model to the slave model.
8. The black start modeling method for driving multiple auxiliary machines by considering a single power supply according to claim 1, characterized in that: in step S3, a waveform diagram is used to show the transient response characteristic of the black start process.
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