CN111786386A - Control system and method for preventing direct current blocking based on transient energy method - Google Patents
Control system and method for preventing direct current blocking based on transient energy method Download PDFInfo
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention relates to a control system and a control method for preventing direct current blocking based on a transient energy method, belongs to the technical field of power systems, and solves the problems that in the prior art, the transient stability performance of a power system is adjusted slowly, and the provided fault clearing time is short. The system comprises a data acquisition module, a data acquisition module and a data processing module, wherein the data acquisition module is used for acquiring electrical data when a multi-machine power system containing HVDC fails; the system transient disturbed trajectory prediction module predicts the rotor angle and the rotor angular speed of the generator after the fault according to the electrical data during the fault; the system transient energy stability domain estimation module is used for obtaining the transient energy stability margin of the multi-machine power system; and when the fault of the multi-machine power system is judged, the transient stability direct current additional controller carries out self-adaptive control on the multi-machine power system according to the transient energy stability margin and the target transient energy stability margin. The system can provide sufficient time to ensure that system faults are removed under the condition that the direct current of the system is not locked, and the safe and stable operation of the system is maintained.
Description
Technical Field
The invention relates to the technical field of power systems, in particular to a control system and a control method for preventing direct current blocking based on a transient energy method.
Background
The high-voltage direct-current transmission line in China has high transmission power and plays an extremely important role in energy transfer distribution, and an alternating-current and direct-current power system in China is in a form of strong direct-current and weak direct-current. The direct current of the high-voltage direct current transmission line is locked, so that the tidal current of an alternating current line is redistributed, the impact on the safe and stable operation of a power system is great, a large amount of power supply load loss can be caused, and the interlocking safety accidents of the system can be further induced. Therefore, the direct current locking measures of the alternating current and direct current interconnection system must be taken carefully.
The direct current circuit has rapid transient regulation and control capability and is an effective means for carrying out safe and stable control on the power system. At present, a constant current control is adopted on a rectifying side of a direct current system, and a constant arc-extinguishing angle control is adopted on an inverting side of the direct current system. When an inverter side alternating current system breaks down, alternating current voltage at an inverter side current conversion bus is distorted, amplitude is greatly reduced, direct current voltage is correspondingly reduced, and if direct current power is still controlled at a rated value, direct current can be rapidly increased to damage system operation. Therefore, when the amplitude of the Voltage of the inversion side commutation bus is greatly reduced, the direct current system adopts a low-Voltage current-limiting control strategy (VDCOL) to ensure the safe operation of the direct current system. Therefore, during the fault period of the alternating current system, selecting proper parameters for the VDCOL is beneficial to improving the stability of the system. The conventional VDCOL control strategy is to limit the dc current of the system when the voltage drops to a certain threshold. In addition, the current time delay of the direct current blocking criterion caused by the alternating current line fault mainly considers the influence of the phase change failure on the transient stability of the whole power system, and the action delay is given through a large number of simulation experiments.
The prior art has at least the following defects that firstly, the traditional VDCOL control strategy needs to be controlled only when the voltage drops to a certain threshold value, the rapid regulation and control of the transient stability performance of a system when the commutation failure is caused by the fault of an alternating current system cannot be met, and sufficient fault clearing time cannot be provided; secondly, the existing direct current blocking criterion time delay mainly considers the influence of commutation failure on the transient stability of the whole power system, and the action delay is given through a large number of simulation experiment results, so that the current state of the power system cannot be fully reflected, and the direct current blocking of the power system cannot be accurately controlled.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a control system and method for preventing dc blocking based on a transient energy method, so as to solve the problems of slow speed of regulating and controlling the transient stability of the system and inaccurate control of dc blocking in the control strategy of the power system in the prior art.
In one aspect, the invention provides a transient energy method-based control system for preventing DC blocking, which comprises
The data acquisition module is used for acquiring electrical data when a multi-machine power system containing HVDC fails; the electrical data comprises rotor angles, rotor angular speeds and electromotive forces of a plurality of generators, voltages of load buses and mutual admittance and self-admittance among nodes of the network topology structure;
the system transient disturbed track prediction module is used for predicting the rotor angle and the rotor angular speed of the generator after the fault according to the rotor angle and the rotor angular speed of the generator during the fault;
the system transient energy stability domain estimation module is used for obtaining the transient energy stability margin of the multi-machine power system according to the predicted rotor angle and rotor angular speed of the generator, the electromotive force of the generator, the voltage of each load bus and the mutual admittance and self-admittance among nodes of the network topology structure; the transient energy stability margin is used for judging whether the multi-machine power system fails;
and the transient stability direct current additional controller is used for carrying out self-adaptive control on the multi-machine power system according to the transient energy stability margin and the target transient energy stability margin so as to maintain the stable operation of the multi-machine power system when the multi-machine power system is judged to have a fault.
Further, the data acquisition module is also used for acquiring direct current of the multi-machine power system after a fault occurs; the transient stability direct current additional controller is also used for carrying out self-adaptive control according to the direct current of the multi-machine power system after the fault occurs and the target direct current so as to stabilize the direct current of the multi-machine power system.
Further, the transient stability direct current additional controller is further configured to obtain an inversion side arc-quenching angle in a self-adaptive control process, and perform real-time online control on the inversion side arc-quenching angle of the HVDC converter according to the inversion side arc-quenching angle.
Further, the system transient energy stability domain estimation module obtains the transient energy stability margin of the multi-machine power system by:
acquiring a leading unstable balance point after the multi-machine power system fails and a corresponding rotor angle and rotor angular speed of each generator;
obtaining the electromagnetic output power of a generator terminal of the corresponding generator according to the predicted rotor angle of the generator, the electromotive force of the generator, the voltage of a load bus and the mutual admittance and self-admittance among nodes of the network topology structure;
obtaining a power difference value of the generator according to the generator-end electromagnetic output power of the generator and the mechanical input power of a prime mover of the generator;
obtaining critical transient state energy of the multi-machine power system according to a unit inertia constant, a power difference value, a rotor angle in fault, a rotor angular speed at a leading unstable balance point and a rotor angle of each generator;
acquiring real-time total energy and real-time kinetic energy of a multi-machine power system after a fault occurs according to a unit inertia constant, a power difference value, a real-time rotor angular velocity after the fault occurs, a real-time rotor angle and a rotor angle during the fault of each generator;
and obtaining the transient energy stability margin of the multi-machine power system according to the critical transient energy, the real-time total energy and the real-time kinetic energy of the multi-machine power system after the fault occurs.
Further, determining a dominant unstable balance point after the multi-machine power system fails, and obtaining a rotor angle and a rotor angular speed of each generator corresponding to the dominant unstable balance point by the following method:
obtaining the minimum gradient value of a gradient system model corresponding to the multi-machine power system after the fault according to the predicted rotor angular speed and rotor angle of the generator;
determining a dominant unstable balance point of the gradient system model on a critical transient state energy boundary and a corresponding rotor angle and rotor angular speed of each generator by utilizing the power balance of the multi-machine power system after the fault based on the minimum gradient value;
and determining a dominant unbalance stable point of the multi-machine power system after the fault and a corresponding rotor angle and a corresponding rotor angular speed of each generator according to a mapping relation between the multi-machine power system and the corresponding gradient system model after the fault.
Further, the mapping relationship is that on a critical transient energy boundary, a dominant imbalance stable point between a stable boundary of the gradient system model and a stable boundary of the multi-machine power system and a corresponding rotor angle and rotor angular velocity of each generator are in one-to-one correspondence.
Further, the system transient disturbed trajectory prediction module predicts the rotor angle and the rotor angular speed of the generator after the fault through a self-memory model:
wherein, wt、θtObtaining rotor angular speed and rotor angle, w, of the generator for prediction, respectivelyi、θiRespectively representing the rotor angular velocity and the rotor angle at the fault acquired at the ith sampling moment, αi、αi' denotes self-memory coefficients corresponding to the i-th sampling rotor angular velocity and rotor angle, respectively, i-p, …,0,1, p is a backtracking coefficient, Δ t denotes a sampling time interval, FiAnd Fi'minute' toDynamic kernels representing rotor angular velocity and rotor angle, respectively.
In another aspect, the present invention provides a control method for preventing dc blocking based on a transient energy method, including:
s1, collecting electrical data when a multi-machine power system containing HVDC fails; the electrical data comprises rotor angles, rotor angular speeds and electromotive forces of a plurality of generators, voltages of load buses and mutual admittance and self-admittance among nodes of the network topology structure;
step S2, predicting the rotor angle and the rotor angular speed of the generator after the fault according to the rotor angle and the rotor angular speed of the generator during the fault;
step S3, obtaining transient energy stability margin of the multi-machine power system according to the predicted rotor angle and rotor angular velocity of the generator, the electromotive force of the generator, the voltage of each load bus and the mutual admittance and self-admittance between each node of the network topology; the transient energy stability margin is used for judging whether the multi-machine power system fails;
and step S4, when the multi-machine power system is judged to be in fault, carrying out self-adaptive control on the multi-machine power system according to the transient energy stability margin and the target transient energy stability margin so as to maintain the stable operation of the multi-machine power system.
Further, the method also comprises the steps of collecting the direct current of the multi-machine power system after the fault occurs, carrying out self-adaptive control according to the direct current of the multi-machine power system after the fault occurs and the target direct current so as to stabilize the direct current of the multi-machine power system, and
and obtaining an inversion side arc-quenching angle in the self-adaptive control process, and carrying out real-time online control on the inversion side arc-quenching angle of the HVDC according to the inversion side arc-quenching angle.
Further, obtaining the transient energy stability margin of the multi-machine power system according to the predicted rotor angle and rotor angular velocity of the generator, the electromotive force of the generator, the voltage of each load bus, and the mutual admittance and self-admittance between each node of the network topology, including:
acquiring a leading unstable balance point after the multi-machine power system fails and a corresponding rotor angle and rotor angular speed of each generator;
obtaining the electromagnetic output power of a generator terminal of the corresponding generator according to the predicted rotor angle of the generator, the electromotive force of the generator, the voltage of a load bus and the mutual admittance and self-admittance among nodes of the network topology structure;
obtaining a power difference value of the generator according to the generator-end electromagnetic output power of the generator and the mechanical input power of a prime mover of the generator;
obtaining critical transient state energy of the multi-machine power system according to a unit inertia constant, a power difference value, a rotor angle in fault, a rotor angular speed at a leading unstable balance point and a rotor angle of each generator;
acquiring real-time total energy and real-time kinetic energy of a multi-machine power system after a fault occurs according to a unit inertia constant, a power difference value, a real-time rotor angular velocity after the fault occurs, a real-time rotor angle and a rotor angle during the fault of each generator;
and obtaining the transient energy stability margin of the multi-machine power system according to the critical transient energy, the real-time total energy and the real-time kinetic energy of the multi-machine power system after the fault occurs.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
1. the method estimates the energy transient stability margin of the multi-machine power system after the fault according to the electrical data when the multi-machine power system is in fault, and utilizes the transient stability direct current additional controller to quickly regulate and control the multi-machine power system according to the energy transient stability margin so as to maintain the stable operation of the multi-machine power system.
2. The method carries out rapid self-adaptive control on the multi-machine power system based on the estimated energy transient stability margin and the target energy transient stability margin of the multi-machine power system, provides sufficient time for removing the fault, effectively ensures that the fault is removed under the condition that the direct current of the multi-machine power system is not locked, and recovers the safe and stable operation of the system.
3. The invention also provides a real-time direct current blocking criterion, after the self-adaptive control is finished, if the fault is not removed, the real-time direct current blocking criterion is used for judging whether the direct current blocking condition is met or not according to the energy transient stability margin of the multi-machine power system when the self-adaptive control is finished, and if the direct current blocking condition is met, the direct current blocking is started to provide double protection for the multi-machine power system, so that the multi-machine power system is effectively prevented from being damaged.
4. The method is based on the direct current of the multi-machine power system and the target direct current, utilizes the transient stability direct current additional controller to carry out self-adaptive control so as to stabilize the direct current of the multi-machine power system, obtains the inversion side arc-quenching angle in the self-adaptive control process, and carries out real-time online control on the inversion side arc-quenching angle of the HVDC according to the inversion side arc-quenching angle.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a schematic diagram of a multi-machine power system including HVDC in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of a control system for preventing DC blocking according to an embodiment of the present invention based on a transient energy method;
FIG. 3 is a schematic diagram of a gradient system model according to an embodiment of the present invention;
FIG. 4 is a flowchart of an alternating current/direct current transient power flow alternating iteration method according to an embodiment of the present invention;
FIG. 5 is a flowchart illustrating a control procedure for preventing DC blocking according to transient energy stability margin of a multi-machine power system according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a transient stability DC supplementary controller according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of the current-voltage characteristics of a conventional low-voltage current-limiting control;
FIG. 8 is a flowchart of a control method for preventing DC blocking according to an embodiment of the present invention based on a transient energy method;
FIG. 9 is a schematic diagram of the prediction result of the transient unstable trajectory of the generator rotor angle in the multi-machine power system according to the embodiment of the present invention;
FIG. 10 is a schematic diagram of a prediction result of a transient stable trajectory of a generator rotor angle of an electromechanical power system in accordance with an embodiment of the present invention;
FIG. 11 is a schematic diagram illustrating the variation of transient energy stability margin of a multi-machine power system when a transient-stable DC additional controller is used according to an embodiment of the present invention;
fig. 12 is a schematic diagram illustrating the transient energy stability margin variation of a multi-machine power system when the transient stability dc additional controller is not used according to an embodiment of the present invention.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
The online application of the transient stability analysis of the power system based on the wide-area information depends on the wide-area communication technology of the power system. On-line safety and stability analysis is the most suitable method for the stability control of the power system, but is limited by the communication equipment and the computer power in the past to realize engineering practical application. Network communication technology and computer computing power have been rapidly developed. The emerging scientific technologies provide a solid foundation for online safety and stability analysis of the power system, and online transient stability analysis based on wide-area information is possible.
An exemplary multi-machine power system comprising HVDC (high voltage direct current transmission system) is shown in fig. 1, G1、G2、G3、G4、G5、G6、G7、G88 synchronous generators of a multi-machine power system, respectively, wherein G1、G2、G3、G4In a group, G5、G6、G7、G8And the alternating current and direct current interconnection among the generators in each group is realized through a rectifier and an inverter of the HVDC. It should be noted that the number and grouping of synchronous generators in a multi-machine power system is for illustration only.
System embodiment
The invention discloses a control system for preventing direct current blocking based on a transient energy method. As shown in fig. 2, comprises
And the data acquisition module is used for acquiring electrical data when the multi-machine power system containing the HVDC fails. The electrical data includes rotor angles, rotor angular velocities, and electromotive forces of the multiple generators, voltages of load buses, and mutual admittance and self-admittance between nodes of the network topology, specifically, voltages of the load buses, that is, bus voltages at a load a and a load B in fig. 1, the mutual admittance includes mutual conductance and mutual admittance between the nodes, and the self-admittance includes self-conductance and self-admittance of the nodes. Wherein, each node includes generator inner node and load node.
And the system transient disturbed track prediction module predicts the rotor angle and the rotor angular speed of each generator after the fault according to the rotor angle and the rotor angular speed of each generator during the fault.
And the system transient energy stability domain estimation module is used for obtaining the transient energy stability margin of the multi-machine power system according to the predicted rotor angle and rotor angular speed of each generator, the electromotive force of each generator, the voltage of each load bus and the mutual admittance and self-admittance between each node of the network topology structure. And judging whether the multi-machine power system has faults or not by using the obtained transient energy stability margin.
And the transient stability direct current additional controller is used for carrying out self-adaptive control on the multi-machine power system according to the transient energy stability margin and the target transient energy stability margin so as to maintain the stable operation of the multi-machine power system when judging that the multi-machine power system has faults.
Preferably, the data acquisition module is further configured to acquire the direct current of the multi-machine power system after the fault occurs. And the transient stability direct current additional controller also performs self-adaptive control according to the direct current of the multi-machine power system after the fault occurs and the target direct current so as to stabilize the direct current of the multi-machine power system.
Preferably, the transient-stable direct-current additional controller is further configured to obtain an inversion side arc-quenching angle in the adaptive control process, and perform real-time online control on the inversion side arc-quenching angle of the HVDC according to the inversion side arc-quenching angle.
Specifically, before each module of the control system operates, firstly, a transient energy function of the multi-machine power system used by the system transient energy stable domain estimation module and a stable domain estimation model based on an unstable point method need to be established, and a self-memory grey Verhulst model used by the system transient disturbed trajectory prediction module needs to be established.
First, a transient energy function of the multi-machine power system is established as follows.
The equation of motion of the rotor of the multi-machine power system is as follows:
wherein, i represents the ith generator, i is 1,2,3, …, n, n is the number of the generators; thetaiIs the ith generator rotor angle relative to the stationary frame,ithe rotor angle of the ith generator relative to a synchronous rotating coordinate system, wherein the rotating speed of the synchronous rotating coordinate system is the same as that of a rotating magnetic field generated by a stator of the generator, and the rotating speed of the synchronous rotating coordinate system is equal to the rated rotor angular speed of the generator under the normal operation of a power system; omegaiThe angular speed deviation of the ith generator rotor relative to the rated angular speed of the generator rotor; omega0Is the rated rotor angular speed of the generator; f. ofiFrequency of the i-th generator, f0Is the synchronous frequency of the generator; pmiMechanically inputting power to a prime mover of the ith generator; peiOutputting power for the terminal electromagnetism of the ith generator; mi is the unit inertia constant of the ith generator, Mi＝TJi/ω0，TjiThe inertia time constant of the ith generating set is represented by the following physical values: the time required to accelerate the rotor of the synchronous generator from 0 to the rated speed under the action of the rated torque.
The electromagnetic power Pei at the generator end can be obtained by the following formula:
in the formula, Cij＝EiEjBij，Dij＝EiEjGij，ij＝i-j，il＝i-l，Yij＝Gij+jBij，i,j∈nG；Yil＝Gil+jBil，i∈nG,l∈nD；EiIs the electromotive force of the ith generator, GijFor the mutual conductance between the ith and jth generators, GilFor the mutual conductance between the ith generator and the l load bus, GiiIs the self-conductance of the ith generator, BijFor mutual susceptance between the ith and jth generators, BilFor mutual susceptance between the ith generator and the ith load bus, UlThe voltage of the l load bus.ijIs the difference between the rotor angles of the ith generator and the jth generator,ilis the phase angle difference between the electromotive force of the ith generator and the voltage of the l load bus, nGNumber of generator nodes in network towing topology for multi-machine power systemDIs the number of load nodes.
Representing a generator rotor motion equation of the multi-machine power system by using the angle of the generator rotor and the deviation amount of the rotor angular speed relative to the rated angular speed:
obtaining the rotor motion equation corresponding to n generators in the multi-machine power system:
defining the inertia center of the multi-machine power system as follows:
in the formula (I), the compound is shown in the specification,
and is
Defining the angle theta of the ith generator rotor relative to the inertia center of the multi-machine power systemi＝i-0And has the following equation:
thereby obtaining a rotor motion equation of the multi-machine power system under the inertial center coordinate:
in the formula, PCOIAfter the disturbance of the multi-machine power system disappears, the acceleration of the angle center,
from equation (6) we can obtain:
in the formula, tcIndicating the time of failure of the multi-machine power system.
For n synchronous generators of a multi-machine power system, summing two ends of the formula (7) respectively to obtain:
equation (8) is related to
In parallel, the following expression can be obtained:
transforming equation (9) yields:
wherein, θ (t)s) The rotor angle at which the fault occurs, θ (t)c) To remove the rotor angle at the moment of the fault.
In the formula (10), the leftmost term
Representing the total energy accumulated in the fault of the multi-machine power system, the term in the middle of the equation
The total energy of the multi-machine power system is constant after the fault is shown, the energy conservation law is satisfied, and the rightmost term
When the fault of the multi-machine power system is recovered to a stable balance point after the fault disappears, the total energy of the multi-machine power system is the total kinetic energy of the rotor moving relative to the inertia center accumulated in the disturbance process of the generator set. At this time, we can obtain the transient energy function of the multi-machine power system containing the HVDC as follows:
or
In the formula, theta (t) represents the real-time rotor angle of the generator, and theta (t)s) Indicating the rotor angle of the generator at the time of the fault,
representing the real-time rotor angular velocity of the generator, wherein,
further, the transient energy function of the multi-machine power system is obtained as follows:
wherein the content of the first and second substances,
secondly, the multi-machine power system has a certain time lag, and if the stable control of the multi-machine power system is to be realized, the system state must be predicted in advance, and a system control command signal is given in advance, so that the aim of real-time decision-making implementation control of the system can be realized. The transient stability of the power system can be evaluated in advance only by predicting the rotor angle and the rotor angular speed of the generator, and then the rapid transient stability control is realized. The power system transient stability disturbed trajectory prediction analysis is essentially to analyze a set of time series data. The grey system theory is an effective method for predicting a time sequence, and a grey Verhulst model is a typical grey prediction model and is mainly applied to scientific prediction of an S-type sequence. The self-memory gray Verhulst model can contain a plurality of historical data of the system, reflect the state relation before and after the system and eliminate the influence of the randomness fluctuation of the system on the prediction result. The actual multi-machine power system is influenced by a plurality of uncertain external factors, so that the randomness and the fluctuation are high, and the difficulty is increased for the disturbed track prediction. On the other hand, the disturbed locus of the multi-machine power system also has an S-shaped characteristic, and for this purpose, a grey Verhulst model with self-memory can be adopted to predict the disturbed locus of the generator rotor angle and the rotor angular speed.
Specifically, a self-memory gray Verhulst model was obtained in the following manner.
The self-remembering dynamic equation is as follows:
in the formula, x is an independent variable, lambda is a parameter, t is time, and F (x, lambda, t) is a dynamic kernel.
The inner product operation is defined as:
T＝{t-p,t-p+1,…,t-1,t0,t1the time set is a time set, and the time set corresponding to the historical observation data is T0＝{t-p,t-p+1,…,t-1,t0Introducing a self-memory coefficient β (t), and substituting the self-memory coefficient β (t) into a self-memory dynamic equation (15) and an inner product operation (16) to obtain:
by performing the piecewise integration of equation (17), we can obtain:
m is the amount of historical data collected, let βi＝β(ti)，xi＝x(1)(ti)，x1＝x(1)(t1)，
The self-memory prediction model was obtained as follows:
order to
Fi＝Fi(x,λ,ti) Further, expressing equation (19) as a discrete expression obtains the model as:
in the formula, αi＝βi/(β1+β0) And i is-p, …,0,1, which is a self-memory coefficient.
And 2, solving the established self-memory model to obtain a self-memory gray Verhulst model suitable for the multi-machine power system.
Training the model by using M historical data, specifically, taking M-p-1 historical data as model input, namely taking vector M, and taking p +1 historical data as model output, namely vector XtTraining obtains the self-memory coefficients α of the model, i.e., vector A, where m>p。
Xt＝MA
The ridge regression solution for vector a is:
A＝(MTM+kI)-1MTXt，
where kI denotes a very small identity matrix, usually k takes 0, so that MTM is reversible.
And determining a self-memory coefficient alpha in the discrete expression so as to obtain a self-memory gray Verhulst model suitable for the multi-machine power system.
And predicting the rotor angle and the rotor angular speed of the generator after the fault according to the model.
The specific process of establishing the stable region estimation model based on the unstable point method is as follows.
For a multi-machine electric power system classical model under an inertial coordinate, a rotor motion equation of the multi-machine electric power system after a fault is as follows:
in the formula, i is 1,2, …, n, n is the number of generators included in the multi-machine power system.
The transient energy function of the multi-machine power system is as follows:
the transient energy function is derived over time t to obtain:
the torque vector is defined as:
defining potential energy gradient vector as:
according to
And formulae (21) to (23) can be obtained
Because multimachine electric power system transient state energy conservation after the trouble then has:
defining a power balance equation of each generator in the multi-machine power system after the fault as follows:
then there are:
the following can be obtained:
multiplying both sides of equation (28) by ωiThe following can be obtained:
Eliminating all non-HVDC nodes and non-generator internal nodes in the multi-machine power system, and establishing a gradient system model contracted between the generator internal nodes and HVDC reserved nodes, as shown in FIG. 3.
A synchronous generator of a multi-machine power system containing HVDC, the HVDC system, a load model, a power transmission line and the like are reasonably simplified and equivalent respectively. Because the mechanical input power and the transient electromotive force of the motor in the transient process of the synchronous generator are kept unchanged, the power supply nodes such as the synchronous generator and the like also comprise a PV node besides a balance node. The HVDC system utilizes a quasi-steady-state model to enable a rectifying side and an inverting side to be equivalent to a PQ load node and a PQ power node which are influenced by rectifying/inverting side end voltage and control parameters (constant current and constant arc-quenching angle).
The load model is complex due to various load types and more dynamic characteristics, and is equivalent to impedance for node contraction for constant impedance type loads, and is equivalent to a PQ node controlled by the bus voltage of a connection point for loads greatly influenced by the bus voltage of the connection point, so as to obtain a gradient system model corresponding to the multi-machine power system, namely a contracted system model, as shown in fig. 3, the gradient system equation is as follows:
as can be seen, the dimension of the state variable of the original multi-machine power system is changed from 2(n-1) to n-1 through system dimension reduction.
The mapping relation between the balance point and the stable boundary of the multi-machine power system and the corresponding gradient system is as follows, and the unstable balance point of the multi-machine power system after the fault can be found through the gradient system according to the mapping relation, wherein the specific mapping relation is as follows:
on the critical transient energy boundary, dominant unbalance stable points between the stable boundary of the gradient system model and the stable boundary of the multi-machine power system and the corresponding rotor angle and rotor angular speed of each generator are in one-to-one correspondence.
Preferably, the system transient disturbed trajectory prediction module predicts the rotor angle and the rotor angular speed of the generator after the fault through a self-memory model:
wherein, wt、θtObtaining rotor angular speed and rotor angle, w, of the generator for prediction, respectivelyi、θiRespectively representing the rotor angular velocity and the rotor angle at the fault acquired at the ith sampling moment, αi、αi' denotes self-memory coefficients corresponding to the i-th sampling rotor angular velocity and rotor angle, respectively, i-p, …,0,1, p is a backtracking coefficient, Δ t denotes a sampling time interval, FiAnd Fi' denotes the dynamic kernel of rotor angular velocity and rotor angle, respectively.
Preferably, the system transient energy stability domain estimation module obtains the transient energy stability margin of the multi-machine power system by:
step 1.1, obtaining the minimum gradient value of a gradient system model corresponding to the multi-machine power system after the fault according to the predicted rotor angular speed and rotor angle of the generator.
Specifically, the method comprises step 1.11, when the multi-machine power system is on the critical transient energy boundary,
from this, the exit point of the multi-machine power system generator rotor motion trajectory on the critical transient energy boundary after the fault can be determined. Based on formula (6), carrying out integral operation on a rotor motion trajectory of a multi-machine power system in a fault by utilizing a linear multi-step algorithm implicit (Adams-Bashforth-Moulton) algorithm, and calculating an exit point (ExitPoint, EP), namely a rotor angle of a generator, which is marked as thetacAnd the point of the projected track of the fault locus of the multimachine power system on the boundary of the stable domain of the gradient system is shown.
In the formula (6), the superscript 2 indicates that the multi-machine power system is in fault, and the projection of the fault trajectory of the multi-machine power system reaches the first transient potential energy maximum value point, namely the exit point.
And step 1.12, taking the calculated outlet point as an initial point, substituting the predicted rotor angular speed and rotor angle of the generator into a gradient system equation (30) of the multi-machine power system, integrating, and obtaining the minimum gradient value of the gradient system corresponding to the multi-machine power system at the first minimum value point of an integration track.
Step 1.2, determining that the gradient system model is on the critical transient state energy boundary by utilizing the power balance of the multi-machine power system after the fault based on the minimum gradient value, namely an equation (26)
And corresponding rotor angle and rotor angular velocity of each generator. Specifically, the rotor angle of each generator is determined when the determined dominant unstable equilibrium point, i.e. the gradient system model, is on the critical transient energy boundary
Step 1.3, determining a dominant unbalance stable point of the multi-machine power system after the fault according to the mapping relation between the multi-machine power system after the fault and the corresponding gradient system model
And corresponding rotor angle theta (t) of each generatorcr) And rotor angular velocity
Specifically, the electromotive force of the generator, the high voltage of the load bus and the corresponding phase angle can be obtained by alternating iterative calculation of the power flow of the power system containing the HVDC. Preferably, the direct current system parameter calculation is carried out according to the initial value of the node voltage in the network topology structure, and the equivalent value is PQ load or power source node. If the initial value of the voltage at two ends of the direct current system is unknown, the initial value can be defaulted to be a per unit value 1, then iterative correction is carried out, and the amplitude value and the phase angle of the actual voltage of the corresponding node of the system are calculated until the system converges. The specific process is shown in fig. 4.
Step 4, according to the unit inertia constant M of each generatoriPower difference Pi(θi) Rotor angle θ (t) at the time of failures) Dominant rotor angular velocity at unstable equilibrium point
Rotor angle θ (t)cr) Obtaining critical transient energy V of the multi-machine power systemcr：
Step 6, obtaining the transient energy stability margin delta V of the multi-machine power system according to the critical transient energy, the real-time total energy and the real-time kinetic energy of the multi-machine power system after the fault occurs:
preferably, a control flow for preventing dc blocking according to the transient energy stability margin of the multi-machine power system is shown in fig. 5.
According to the obtained transient state energy stability margin of the multi-machine power system, carrying out safety early warning on the multi-machine power system through the following transient state stability margin division indexes:
when the obtained transient energy stability margin of the multi-machine power system is larger than 2, judging that the multi-machine power system is operated safely and stably, and ending the control; and when the transient state energy stability margin is less than or equal to 2, judging that the multi-machine power system has a fault, and taking the transient state stability margin and the target transient state energy stability margin of the multi-machine power system as input control signals of the transient state stability direct current additional controller.
In the process of carrying out self-adaptive control on the multi-machine power system, judging whether the fault of the multi-machine power system is removed or not, if so, keeping the multi-machine power system stable, and ending the control; if not, judging whether the transient energy stability margin of the multi-machine power system meets the direct current blocking criterion of delta V being less than delta Vref，ΔVrefIf the target transient state energy stability margin is not met, carrying out safety early warning on the multi-machine power system again according to the current transient state energy stability margin of the multi-machine power system, and repeating the subsequent work; if yes, starting the DC lock to prevent damage to the multi-machine power system, thereby ensuring the safety of the multi-machine power systemThe stable operation provides double protection.
Meanwhile, the transient stability direct current additional controller also performs self-adaptive control according to the direct current of the multi-machine power system after the fault occurs and a target direct current to stabilize the direct current of the multi-machine power system, wherein the target direct current is the direct current when the multi-machine power system is safely and stably operated before the fault occurs.
Specifically, the transient state energy stability margin and the control process of the direct current of the multi-machine power system by the transient state stable direct current additional controller are shown in fig. 6, the first PI regulator is used for adaptively controlling the transient state energy stability margin of the multi-machine power system, the second PI regulator is used for adaptively controlling the direct current of the multi-machine power system, the first PI regulator comprises a first proportional regulator (K1) and a first integral regulator (K2/s), and the first proportional regulator (K1) is used for reflecting the deviation between the real-time transient state energy stability margin and the target transient state energy stability margin of the multi-machine power system in proportion, and adaptively regulating the transient state energy stability margin of the multi-machine power system according to the proportional information to reduce the deviation, but cannot achieve no difference; the first integral regulator (K2/s) is used for integral regulation of the transient state energy stability margin of the multi-machine power system, eliminating deviation and improving the tolerance, so that the transient state energy stability margin of the multi-machine power system reaches the target transient state energy stability margin, the transient state stability of the multi-machine power system after the fault is realized, and sufficient time is provided for external fault removal. The second PI regulator comprises a second proportional regulator (K3) and a second integral regulator (K4/s) which function in the same manner as the first PI regulator.
Specifically, as shown in fig. 7, the conventional dc system low-voltage current limiting control adopts the following strategies: after the fault, the DC voltage is controlled only when the DC voltage is lower than a fixed value. During the dc voltage drop, when the fault has occurred for a period of time, the dc current may already be large, resulting in dc latch-up. The invention adopts real-time online control, and self-adaptively adjusts the direct current and the transient energy stability margin of the multi-machine power system when the multi-machine power system is detected to have a fault, thereby effectively preventing the direct current locking of the multi-machine power system.
In addition, the output quantity of the transient stable direct current additional controller in the self-adaptive control process is an inversion side arc-quenching angle alpha, and real-time online control is carried out on the inversion side arc-quenching angle of the HVDC according to the inversion side arc-quenching angle alpha, so that the inverter commutation failure is effectively prevented.
Method embodiment
In another embodiment of the present invention, a control method for preventing dc blocking based on the transient energy method is disclosed, as shown in fig. 8. The control method using the control system includes:
and step S1, collecting electrical data when the multi-machine power system containing the HVDC has faults. The electrical data includes rotor angles, rotor angular velocities, electromotive forces of the plurality of generators, voltages of the load buses, and mutual and self-admittances between nodes of the network topology.
Step S2 predicts the rotor angle and rotor angular velocity of each generator after the failure based on the rotor angle and rotor angular velocity of each generator at the time of the failure.
Step S3, obtaining transient energy stability margin of the multi-machine power system according to the predicted rotor angle, rotor angular velocity and electromotive force of each generator, voltage of each load bus and mutual admittance and self-admittance between each node of the network topology structure; and the transient energy stability margin is used for judging whether the multi-machine power system fails.
And step S4, when the multi-machine power system is judged to be in fault, carrying out self-adaptive control on the multi-machine power system according to the transient energy stability margin and the target transient energy stability margin so as to maintain the stable operation of the multi-machine power system.
Preferably, the method further comprises the steps of collecting the direct current of the multi-machine power system after the fault occurs, carrying out self-adaptive control according to the direct current of the multi-machine power system after the fault occurs and a target direct current to stabilize the direct current of the multi-machine power system, wherein the target direct current is the direct current when the multi-machine power system safely and stably operates before the fault occurs, and
and obtaining the inversion side arc-quenching angle in the self-adaptive control process, and carrying out real-time online control on the inversion side arc-quenching angle of the HVDC according to the inversion side arc-quenching angle.
Preferably, in step S3, the obtaining the transient energy stability margin of the multi-machine power system according to the predicted rotor angle, rotor angular velocity, electromotive force of the generator, voltage of each load bus, and mutual and self-admittance between nodes of the network topology includes:
step S3.1, obtaining a leading unstable balance point after the multi-machine power system fails and a corresponding rotor angle and rotor angular speed of each generator, and comprising the following steps:
and S3.11, obtaining the minimum gradient value of the gradient system model corresponding to the multi-machine power system after the fault according to the predicted rotor angular speed and rotor angle of the generator.
Specifically, including step S3.111, when the multi-machine power system is on the critical transient energy boundary,
from this, the exit point of the multi-machine power system generator rotor motion trajectory on the critical transient energy boundary after the fault can be determined. Based on a formula (6), carrying out integral operation on a rotor motion trajectory of a multi-machine power system in a fault by utilizing a linear multi-step algorithm implicit (Adams-Bashforth-Moulton) algorithm, and calculating an Exit Point (Exit Point, EP), namely a rotor angle of a generator, and marking as thetacAnd the point of the projected track of the fault locus of the multimachine power system on the boundary of the stable domain of the gradient system is shown.
In the formula (6), the superscript 2 indicates that the multi-machine power system is in fault, and the projection of the fault trajectory of the multi-machine power system reaches the first transient potential energy maximum value point, namely the exit point.
And step S3.112, taking the calculated exit point as an initial point, substituting the predicted rotor angular speed and rotor angle of the generator into a gradient system equation (30) of the multi-machine power system, integrating, and obtaining the minimum gradient value of the gradient system corresponding to the multi-machine power system at the first minimum value point of an integration track.
Step S3.12, determining that the gradient system model is on the critical transient state energy boundary by utilizing the power balance of the multi-machine power system after the fault based on the minimum gradient value, namely an equation (26)
And corresponding rotor angle and rotor angular velocity of each generator. Specifically, the rotor angle of each generator is determined when the determined dominant unstable equilibrium point, i.e. the gradient system model, is on the critical transient energy boundary
S3.13, determining a dominant unbalance stable point of the multi-machine power system after the fault according to the mapping relation between the multi-machine power system after the fault and the corresponding gradient system model
And corresponding rotor angle theta (t) of each generatorcr) And rotor angular velocity
The specific mapping relationship is as follows:
on the critical transient energy boundary, dominant unbalance stable points between the stable boundary of the gradient system model and the stable boundary of the multi-machine power system and the corresponding rotor angle and rotor angular speed of each generator are in one-to-one correspondence.
S3.2, obtaining the generator end electromagnetic output power P of the corresponding generator according to the predicted rotor angle of the generator, the electromotive force of the generator, the voltage of a load bus and the mutual admittance and self-admittance among nodes of the network topology structure by using a formula (2)ei。
Specifically, the electromotive force of the generator, the high voltage of the load bus and the corresponding phase angle can be obtained by alternating iterative calculation of the power flow of the power system containing the HVDC. Preferably, the direct current system parameter calculation is carried out according to the initial value of the node voltage in the network topology structure, and the equivalent value is PQ load or power source node. If the initial value of the voltage at two ends of the direct current system is unknown, the initial value can be defaulted to be a per unit value 1, then iterative correction is carried out, and the amplitude value and the phase angle of the actual voltage of the corresponding node of the system are calculated until the system converges.
Step S3.3, according to the generator end electromagnetic output power P of the generatoreiAnd prime mover mechanical input power P of said generatormiObtaining a power difference P of the generatori(θi)。
S3.4, according to the unit inertia constant M of each generatoriPower difference Pi(θi) Rotor angle θ (t) at the time of failures) Dominant rotor angular velocity at unstable equilibrium point
Rotor angle θ (t)cr) Obtaining critical transient energy V of the multi-machine power systemcr：
S3.5, according to the unit inertia constant M of each generatoriPower difference Pi(θi) Real-time rotor angular velocity after occurrence of a fault
Real-time rotor angle theta (t) and rotor angle theta (t) at faults) Obtaining real-time total energy V and real-time kinetic energy V after multi-machine electric power system failsK|c：
S3.6, obtaining the transient energy stability margin delta V of the multi-machine power system according to the critical transient energy of the multi-machine power system, the real-time total energy after the fault and the real-time kinetic energy:
preferably, safety early warning is performed on the multi-machine power system through the following transient stability margin division indexes according to the obtained transient energy stability margin of the multi-machine power system:
when the obtained transient energy stability margin of the multi-machine power system is larger than 2, judging that the multi-machine power system is operated safely and stably, and ending the control; and when the transient state energy stability margin is less than or equal to 2, judging that the multi-machine power system has a fault, taking the transient state energy stability margin and the target transient state energy stability margin of the multi-machine power system as control signals, and carrying out self-adaptive control on the multi-machine power system according to the control signals to ensure that the transient state energy stability margin of the multi-machine power system reaches the target transient state energy stability margin, so that the transient state stability of the multi-machine power system is realized, and the direct current blocking is avoided.
In the process of carrying out self-adaptive control on the multi-machine power system, judging whether the fault of the multi-machine power system is removed or not, if so, keeping the multi-machine power system stable, and ending the control; if not, judging whether the transient energy stability margin of the multi-machine power system meets the direct current blocking criterion of delta V being less than delta Vref，ΔVrefIf the target transient state energy stability margin is not met, carrying out safety early warning on the multi-machine power system again according to the current transient state energy stability margin of the multi-machine power system, and repeating the subsequent work; if the voltage is met, the direct current lock is started, so that double protection is provided for safe and stable operation of the multi-machine power system.
The beneficial effects of the present invention are now demonstrated by the following examples. Specifically, a multi-machine power system structure comprising two four-machine two-zone high voltage direct current transmission (HVDC) connections is adopted. As shown in fig. 1. Wherein the DC voltage of the high-voltage DC transmission system is 500kV, and the transmission power is 10And 00 MW. The synchronous generator adopts a classical second-order model, the rated capacity of each generator is 900MVA, the rated voltage is 20kV, the inertia time constant M of the generator is 6.5, and the direct-axis synchronous reactance of the generator is xd1.8, the direct-axis transient reactance is x'd0.3, negative sequence impedance x20.2. Reference capacity of multi-machine power system is SB1000MVA, reference voltage 345 kV.
The embodiment verifies the accuracy of the self-memory gray Verhulst model on transient disturbed trajectory prediction and the feasibility of transient energy method on-line transient regulation. The system simulation model shown in fig. 1 is adopted to improve the simulation system, and a transient stability direct current additional controller is added in the direct current control link, and the result is as follows.
1) Transient disturbed trajectory prediction verification
In this embodiment, a persistent single-phase fault is set at a point a (30% of a line) on the inversion side of the simulation system in fig. 1, and a group of unstable trajectories and stable trajectories are selected for analysis. During prediction, 100ms of sampling data is used as a data window to predict a future 300ms transient disturbance locus. Fig. 9 is a result of predicting a transient unstable trajectory, fig. 10 is a result of predicting a transient stable trajectory, and the maximum error of power angle prediction is within 4.5 °, which all have good prediction effects.
2) Transient stability fast control verification
This embodiment is at t0When the time is 60s, a continuous three-phase short-circuit fault is set at the point A (30% of a line) on the inversion side of the simulation system. At the moment, the inverter side of the direct current system has phase commutation failure, and the direct current system has the rapid transient regulation and control capability. When the transient stability margin index delta V of the system is smaller than 2, the direct current control system starts to put in the transient stability direct current additional controller, so that the rapid reduction of the transient stability margin of the system is delayed as much as possible, namely the accumulation speed of the transient energy in the fault process is restrained. FIG. 11 shows the effect of the DC-plus controller on the transient stability of the system after it is turned on. As can be seen from fig. 12, 170ms after the fault occurs, the transient stability margin of the system is smaller than 2, the direct current command is changed to 0.41, and the transient stability of the system is significantly improved. System critical fault clearing time tcrAbout 406ms, compared to the case without DC attachment as shown in FIG. 10The critical fault clearing time is about 290ms when the controller is applied, which is improved by about 116 ms. Therefore, the transient stability direct current additional controller designed by the invention has a certain transient regulation effect.
In this embodiment, a three-phase short-circuit fault is further set at a position 20% away from the inverter station on the ac line, and the corresponding dc current command value and the fault critical clearing time are shown in table 1. The current command is continuously reduced, and the fault critical clearing time is also continuously increased, namely, the control system and the method for preventing the direct current blocking can effectively prevent the direct current blocking, so that the impact of the direct current blocking on the transient stability of the system is reduced.
TABLE 1 Current Command and Critical cut time
Compared with the prior art, the control system and the method for preventing direct current blocking based on the transient energy method provided by the invention have the advantages that firstly, the energy transient stability margin of a multi-machine power system after failure is estimated according to the electrical data when the multi-machine power system fails, and the transient stability direct current additional controller is used for quickly regulating and controlling the multi-machine power system according to the energy transient stability margin so as to maintain the stable operation of the multi-machine power system; secondly, fast self-adaptive control is carried out on the multi-machine power system based on the estimated energy transient stability margin and the target energy transient stability margin of the multi-machine power system, sufficient time is provided for removing faults, the faults are effectively removed under the condition that the direct current of the multi-machine power system is not locked, and the safe and stable operation of the system is recovered; then, the invention also provides a real-time direct current blocking criterion, after the self-adaptive control is finished, if the fault is not removed, the real-time direct current blocking criterion is used for judging whether the condition of direct current blocking is achieved or not according to the energy transient stability margin of the multi-machine power system when the self-adaptive control is finished, and if the condition is met, the direct current blocking is started to provide double protection for the multi-machine power system, so that the multi-machine power system is effectively prevented from being damaged; finally, the method utilizes the transient stability direct current additional controller to carry out self-adaptive control based on the direct current of the multi-machine power system and the target direct current so as to stabilize the direct current of the multi-machine power system, obtains the inversion side arc-quenching angle in the self-adaptive control process, and carries out real-time online control on the inversion side arc-quenching angle of the HVDC according to the inversion side arc-quenching angle.
Those skilled in the art will appreciate that all or part of the flow of the method implementing the above embodiments may be implemented by a computer program, which is stored in a computer readable storage medium, to instruct related hardware. The computer readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A control system for preventing DC blocking based on a transient energy method is characterized by comprising:
the data acquisition module is used for acquiring electrical data when a multi-machine power system containing HVDC fails; the electrical data comprises rotor angles, rotor angular speeds and electromotive forces of a plurality of generators, voltages of load buses and mutual admittance and self-admittance among nodes of the network topology structure;
the system transient disturbed track prediction module is used for predicting the rotor angle and the rotor angular speed of the generator after the fault according to the rotor angle and the rotor angular speed of the generator during the fault;
the system transient energy stability domain estimation module is used for obtaining the transient energy stability margin of the multi-machine power system according to the predicted rotor angle and rotor angular speed of the generator, the electromotive force of the generator, the voltage of each load bus and the mutual admittance and self-admittance among nodes of the network topology structure; the transient energy stability margin is used for judging whether the multi-machine power system fails;
and the transient stability direct current additional controller is used for carrying out self-adaptive control on the multi-machine power system according to the transient energy stability margin and the target transient energy stability margin so as to maintain the stable operation of the multi-machine power system when the multi-machine power system is judged to have a fault.
2. The control system for preventing direct current blocking according to claim 1, wherein the data acquisition module is further configured to acquire direct current of the multi-machine power system after a fault occurs; the transient stability direct current additional controller is also used for carrying out self-adaptive control according to the direct current of the multi-machine power system after the fault occurs and the target direct current so as to stabilize the direct current of the multi-machine power system.
3. The control system for preventing direct current blocking according to claim 1, wherein the transient stability direct current additional controller is further configured to obtain an inversion side arc-quenching angle in an adaptive control process, and perform real-time online control on the inversion side arc-quenching angle of the HVDC according to the inversion side arc-quenching angle.
4. The dc blocking prevention control system according to claim 1, wherein the system transient energy stability domain estimation module obtains the transient energy stability margin of the multi-machine power system by:
acquiring a leading unstable balance point after the multi-machine power system fails and a corresponding rotor angle and rotor angular speed of each generator;
obtaining the electromagnetic output power of a generator terminal of the corresponding generator according to the predicted rotor angle of the generator, the electromotive force of the generator, the voltage of a load bus and the mutual admittance and self-admittance among nodes of the network topology structure;
obtaining a power difference value of the generator according to the generator-end electromagnetic output power of the generator and the mechanical input power of a prime mover of the generator;
obtaining critical transient state energy of the multi-machine power system according to a unit inertia constant, a power difference value, a rotor angle in fault, a rotor angular speed at a leading unstable balance point and a rotor angle of each generator;
acquiring real-time total energy and real-time kinetic energy of a multi-machine power system after a fault occurs according to a unit inertia constant, a power difference value, a real-time rotor angular velocity after the fault occurs, a real-time rotor angle and a rotor angle during the fault of each generator;
and obtaining the transient energy stability margin of the multi-machine power system according to the critical transient energy, the real-time total energy and the real-time kinetic energy of the multi-machine power system after the fault occurs.
5. The DC blocking prevention control system according to claim 4, wherein a dominant unstable balance point after the multi-machine power system is in failure is determined, and the rotor angle and the rotor angular speed of each generator corresponding to the dominant unstable balance point are obtained by:
obtaining the minimum gradient value of a gradient system model corresponding to the multi-machine power system after the fault according to the predicted rotor angular speed and rotor angle of the generator;
determining a dominant unstable balance point of the gradient system model on a critical transient state energy boundary and a corresponding rotor angle and rotor angular speed of each generator by utilizing the power balance of the multi-machine power system after the fault based on the minimum gradient value;
and determining a dominant unbalance stable point of the multi-machine power system after the fault and a corresponding rotor angle and a corresponding rotor angular speed of each generator according to a mapping relation between the multi-machine power system and the corresponding gradient system model after the fault.
6. The DC blocking prevention control system according to claim 5, wherein the mapping relationship is a one-to-one correspondence between dominant imbalance stabilization points on the stabilization boundary of the gradient system model and the stabilization boundary of the multi-machine power system and the corresponding rotor angle and rotor angular velocity of each generator on the critical transient energy boundary.
7. The dc blocking prevention control system according to claim 1, wherein the system transient disturbed trajectory prediction module predicts a rotor angle and a rotor angular speed of the generator after the fault through a self-memory model:
wherein, wt、θtObtaining rotor angular speed and rotor angle, w, of the generator for prediction, respectivelyi、θiRespectively representing the rotor angular velocity and the rotor angle at the fault acquired at the ith sampling moment, αi、αi' denotes self-memory coefficients corresponding to the i-th sampling rotor angular velocity and rotor angle, respectively, i-p, …,0,1, p is a backtracking coefficient, Δ t denotes a sampling time interval, FiAnd Fi' denotes the dynamic kernel of rotor angular velocity and rotor angle, respectively.
8. A control method for preventing direct current blocking based on a transient energy method is characterized by comprising the following steps:
collecting electrical data when a multi-machine power system containing HVDC fails; the electrical data comprises rotor angles, rotor angular speeds and electromotive forces of a plurality of generators, voltages of load buses and mutual admittance and self-admittance among nodes of the network topology structure;
predicting the rotor angle and the rotor angular speed of the generator after the fault according to the rotor angle and the rotor angular speed of the generator during the fault;
obtaining transient energy stability margin of the multi-machine power system according to the predicted rotor angle and rotor angular speed of the generator, the electromotive force of the generator, the voltage of each load bus and the mutual admittance and self-admittance among nodes of the network topology structure; the transient energy stability margin is used for judging whether the multi-machine power system fails;
and when the multi-machine power system is judged to have a fault, carrying out self-adaptive control on the multi-machine power system according to the transient state energy stability margin and the target transient state energy stability margin so as to maintain the stable operation of the multi-machine power system.
9. The control method for preventing dc blocking according to claim 8, further comprising collecting the dc current of the multi-machine power system after the occurrence of the fault, and performing adaptive control to stabilize the dc current of the multi-machine power system according to the dc current of the multi-machine power system after the occurrence of the fault and a target dc current, and
and obtaining an inversion side arc-quenching angle in the self-adaptive control process, and carrying out real-time online control on the inversion side arc-quenching angle of the HVDC according to the inversion side arc-quenching angle.
10. The control method for preventing dc blocking according to claim 8, wherein obtaining the transient energy stability margin of the multi-machine power system according to the predicted rotor angle, rotor angular velocity and electromotive force of the generator, voltage of each load bus and mutual and self-admittance between nodes of the network topology comprises:
acquiring a leading unstable balance point after the multi-machine power system fails and a corresponding rotor angle and rotor angular speed of each generator;
obtaining the electromagnetic output power of a generator terminal of the corresponding generator according to the predicted rotor angle of the generator, the electromotive force of the generator, the voltage of a load bus and the mutual admittance and self-admittance among nodes of the network topology structure;
obtaining a power difference value of the generator according to the generator-end electromagnetic output power of the generator and the mechanical input power of a prime mover of the generator;
obtaining critical transient state energy of the multi-machine power system according to a unit inertia constant, a power difference value, a rotor angle in fault, a rotor angular speed at a leading unstable balance point and a rotor angle of each generator;
acquiring real-time total energy and real-time kinetic energy of a multi-machine power system after a fault occurs according to a unit inertia constant, a power difference value, a real-time rotor angular velocity after the fault occurs, a real-time rotor angle and a rotor angle during the fault of each generator;
and obtaining the transient energy stability margin of the multi-machine power system according to the critical transient energy, the real-time total energy and the real-time kinetic energy of the multi-machine power system after the fault occurs.
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