CN111740416B - Target cascade analysis-based receiving-end power grid direct-current maximum feed-in quantity evaluation method - Google Patents
Target cascade analysis-based receiving-end power grid direct-current maximum feed-in quantity evaluation method Download PDFInfo
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Abstract
The invention provides a target cascade analysis-based receiving-end power grid direct-current maximum feed-in quantity evaluation method, which comprises the following steps: firstly, analyzing the sensitivity of different load removal on system frequency recovery of a fault point adjacent bus nodes, dividing the load into a high-sensitivity load and a low-sensitivity load, and constructing a lower-layer model; secondly, acquiring a low-frequency suppression strategy of the receiving-end power grid after the high-capacity direct-current bipolar blocking fault according to the frequency characteristic of the receiving-end power grid, and constructing an upper-layer model; and finally, respectively carrying out iterative solution on the upper layer model and the lower layer model by using a target cascade analysis method to obtain the maximum direct current feed-in quantity of the receiving-end power grid. According to the invention, the calculation result can ensure that the load cut by the receiving-end power grid is minimum when the direct-current bipolar latching fault occurs by constructing the lower-layer model, so that the benefit of a power consumer is ensured to the maximum extent; the method utilizes the GAMS platform to carry out modeling and calls the solver to solve, so that the model solving process is simple, quick and effective.
Description
Technical Field
The invention relates to the technical field of planning design and scheduling operation of a power system, in particular to a receiving-end power grid direct-current maximum feed-in quantity evaluation method based on target cascade analysis.
Background
The area of Chinese is large, and the energy distribution and the load demand of the Chinese show remarkable asymmetric characteristics. The imbalance of energy distribution and productivity layout determines the need of long-distance and large-capacity power transmission in China. Because the extra-high voltage direct current has the natural advantages of large transmission capacity, long power transmission distance, low line loss and the like, the extra-high voltage direct current becomes a main mode of 'west-east power transmission', and the trans-regional consumption of clean energy and the optimal configuration of resources are realized.
Although the problem of clean energy delivery in northwest areas and power shortage in middle-east areas is solved by the ultra-high voltage direct current transmission, a new challenge is brought to dispatching and operation of receiving-end power grids in middle-east areas. When a bipolar locking fault occurs in high-capacity direct current, a large amount of power shortage occurs in a receiving-end power grid, so that the system frequency is rapidly reduced, and a third defense line action such as low-frequency load shedding of the receiving-end power grid is triggered when the system frequency is serious. Therefore, the problem of frequency stability of the receiving-end power grid is obvious under the condition of multiple direct current intensive feed-in patterns. In order to ensure safe and stable operation of a receiving-end power grid, the maximum direct current feed-in quantity of the receiving-end power grid needs to be evaluated from the view points of inertia and frequency stability.
At present, the related technology only relates to the analysis and calculation of the maximum direct current feed-in quantity of the regional connection in a synchronous networking state, and no method for evaluating the maximum direct current feed-in quantity of the receiving-end power grid, which directly meets the frequency stability requirement of the receiving-end power grid under a high-capacity intensive direct current feed-in pattern, exists.
Disclosure of Invention
Aiming at the defects in the background technology, the invention provides a receiving-end power grid direct-current maximum feed-in quantity evaluation method based on target cascade analysis, and solves the technical problem that the existing regional connecting line maximum transmission capacity evaluation method only aims at the synchronous networking state and cannot evaluate the receiving-end power grid direct-current maximum feed-in quantity under a large-capacity intensive direct-current feed-in pattern.
The technical scheme of the invention is realized as follows:
a receiving-end power grid direct-current maximum feed-in quantity evaluation method based on target cascade analysis comprises the following steps:
s1: analyzing the sensitivity of different types of load removal of the adjacent bus nodes of the fault point to the frequency recovery of the receiving-end power grid system, and dividing the load into a high-sensitivity load and a low-sensitivity load;
s2: acquiring a low-frequency suppression strategy of a receiving-end power grid after a high-capacity direct-current bipolar blocking fault according to the frequency characteristic of a receiving-end power grid system;
s3: constructing an upper layer model according to the low-frequency suppression strategy in the step S2;
s4: constructing a lower layer model according to the high sensitivity load and the low sensitivity load in the step S1;
s5: and respectively carrying out iterative solution on the upper layer model and the lower layer model by using a target cascade analysis method to obtain the maximum direct-current feed-in quantity of the receiving-end power grid.
The method for analyzing the sensitivity of the fault point adjacent bus node on system frequency recovery by different load removal comprises the following steps:
s11: setting that the sensitivity of the system to frequency recovery and fluctuation is the same when all loads of adjacent bus nodes of a fault point are removed;
s12: setting an expected accident set which comprises r typical faults, and acquiring a frequency curve f' of the system after the load corresponding to the fault p is removed by using electromechanical simulation software BPA, wherein the typical faults comprise a three-phase short circuit, a single-phase short circuit, a two-phase grounding short circuit, a direct-current single-pole latch, a direct-current double-pole latch and a generator set trip;
s13: for the same fault p, cutting off the load with the same capacity as the synchronous generator set corresponding to the same fault p on the adjacent node of the same fault p, and acquiring a frequency curve f' of the system by using electromechanical simulation software;
s14: respectively carrying out equally-spaced discrete processing on the frequency curves f 'and f' and calculating the offset coefficient alpha of the adjacent nodes with the same fault p:
wherein n 'is an interval, n' is 1,2, …, 3000;
s15: respectively calculating the average deviation coefficient alpha of the loads of the adjacent nodes to the expected accident setaveAnd by the magnitude versus average offset coefficient alphaaveThe load of the nodes adjacent to the fault point is divided into high-sensitivity load and low-sensitivity load through a set division threshold value.
The low-frequency suppression strategy is a coordination strategy of primary frequency modulation, direct-current modulation and accurate load shedding, and the specific strategy is as follows:
s21: at the moment of failure, the direct current emergency power supports rapid action, and part of blocking power of the failed direct current is transferred to a non-failed direct current connecting line; meanwhile, the load shedding device acts, and the unbalanced power of the system is reduced as follows:
wherein the content of the first and second substances,
indicates the unbalanced power of the transmission network at the moment of bipolar latch-up occurrence,. DELTA.PL'tShowing the unbalanced power after the DC modulation and load shedding action of the system, wherein Δ PLS is the total load after fault shedding, and Δ PHChThe modulation quantity of the h-th non-fault direct current is, h is the non-fault direct current, and l is a fault direct current line;
the constraint conditions met by the direct current power modulation quantity are as follows:
the load shedding amount satisfies the constraint conditions:
wherein the content of the first and second substances,
represents the upper limit value of the transmission power of the h-th non-fault direct current,
representing the maximum emergency modulation quantity of the h-th non-fault direct current, and rho representing the overload proportion allowed by the short-term direct current modulation;
s22: the transmission power of the h-th non-fault DC participating in emergency power support is kept at a constant value PHC within the primary frequency modulation response timeh+△PHCh；
S23: when the frequency deviation of the system exceeds the dead zone of the frequency of the generator, all synchronous generator sets participating in primary frequency modulation gradually release rotation for standby application to increase output force, so that the unbalanced power of the system is reduced until the frequency of the system reaches a quasi-steady state.
The upper layer model comprises an upper layer objective function and upper layer constraint conditions, wherein the upper layer constraint conditions comprise a receiving end power grid frequency stability constraint, a receiving end power grid operation constraint, a direct current tie line power constraint and an upper layer load shedding constraint;
the upper-layer objective function is to maximize the direct current feed-in quantity of a receiving-end power grid:
wherein, TTCtTransmission power, alpha, representing a period of tt、γtAll represent a penalty factor,. DELTA.PLStThe amount of the load to be cut is shown,
representing the optimal load reduction amount of the lower model, wherein t is the moment;
the receiving end power grid frequency stabilization comprises frequency change rate constraint and extreme value frequency constraint;
the frequency rate of change constraint is:
wherein the content of the first and second substances,
representing the unbalanced power, RoCoF, after system DC modulation and load shedding actiontRepresenting the rate of change of frequency of the sending-end grid during time t,
representing the inertia level of the system during the t period, RoCoFmaxRepresents a tolerable maximum value of the rate of change of frequency,
PHC representing the instantaneous unbalanced power of the transmitting grid at the moment of bipolar blockingt,lRepresenting the transmission power of the fault direct current line l before locking;
representing the maximum output, f, allowed by the synchronous unit i0System frequency, H, representing the moment of failureiRepresenting the inertia level, Δ PLS, of the synchronous unit itIndicates the total cutter amount, Δ PHC, of the t periodt,hRespectively representing the modulation power of the h-th non-fault direct current in the t period;
the extreme frequency constraint is:
wherein rr isiRepresenting the climbing rate of the synchronous unit i; f. ofminRepresenting the low-frequency deloading operating frequency, f, of the receiving-end griddbThe frequency dead zone of a receiving-end power grid is shown, and the delta PLS is the total load after the fault is removed;
representing a primary frequency modulation up-regulation standby value of a synchronous unit i in a scene u at a time period t;
the receiving end power grid operation constraint comprises active power balance constraint, transmission power constraint of a power transmission line, unit output/climbing constraint, rotation standby constraint and normal state operation constraint;
the active power balance constraint is:
wherein PGt,i,uRepresents the output, PW, of the synchronous unit i in the t period under the scene ut,j,uRepresents the output, PD, of the wind turbine set j in the time period t under the scene ut,dRepresenting the active demand, PHC, of load d during time tt,hRepresenting the transmission power of the h-th non-fault direct current in a t period;
the transmission power constraint of the transmission line is as follows:
wherein, SFb,nRepresenting the power transfer factor, KGb,iIndicating node association factor, KW, of synchronous setsb,jRepresenting node association factor, KD, of a wind turbineb,dA node association factor representing the load,
representing the maximum transmission capacity allowed by the nth AC line in the receiving end power grid;
the unit output/climbing constraints are:
wherein the content of the first and second substances,
represents the maximum output allowed by the wind turbine j,
represents the minimum output allowed by the synchronization group i,
represents the maximum output allowed by the synchronous unit i,
indicating a ramp down limit for the synchronous unit i,
indicating the uphill limit of the synchronized group i,
indicating that the synchronous unit i in the scene u adjusts the standby value in the primary frequency modulation of the t-th time period,
representing a scene u2The output of the lower synchronous unit i in the t-th time period,
representing a scene u3Lower synchronizerThe output of group i during the t-th period,
representing a scene u2The output of the lower synchronous machine set i in the t-1 th time period,
respectively representing a presentation scene u3The output of the lower synchronous unit i in the t-th time period;
the rotational standby constraints are:
wherein the content of the first and second substances,
representing the maximum value of the primary frequency modulation up-regulation reserve of the synchronous unit i;
the normal state operating constraints are:
wherein the content of the first and second substances,
represents the minimum transmission power of the h-th non-faulty dc,
representing the maximum transmission power of the h-th non-fault direct current;
the direct current tie line power constraint comprises a direct current power adjustment stepped constraint, an adjacent time interval non-backward adjustment constraint, a direct current tie line all-day adjustment frequency constraint and a direct current tie line emergency power support constraint;
the step constraint of the direct current power adjustment is as follows:
wherein, Δ PHCt,hThe power adjustment quantity of the h non-fault direct current in the t period after the fault occurs is shown,
a limit value representing the h-th non-faulted dc single-trip down-regulation,
a limit value representing the h-th non-faulted dc one-time up-adjustment amount,
indicating the rising edge of the power adjustment step for the h-th non-failing dc during the t period,
indicating the falling edge of the power adjustment step of the h-th non-fault DC in the t period, It,hIndicating the operating state of the h-th non-fault DC in the period t, It-1,hIndicating the operation state of the h-th non-fault direct current in the t-1 period,
the shortest continuous operation time of the h-th non-fault direct current at a certain power level is represented;
the adjacent time period must not be adjusted reversely and is constrained as follows:
wherein the content of the first and second substances,
indicating the rising edge of the power adjustment step for the h-th non-failing dc during the t-1 period,
the power adjustment step of the h-th non-fault direct current in the t-1 period is shown;
the constraint of the whole-day adjustment times of the direct current tie line is as follows:
wherein phi ishThe h-th non-fault direct current all-day adjustment frequency upper limit is represented, and T represents the total time period number;
the direct current tie line emergency power support constraints are:
wherein, rho represents the overload ratio allowed by the short-term direct current modulation;
the upper layer shear load constraint is as follows:
△PLSt≤△PLSmax。
the lower layer model comprises a lower layer objective function and lower layer constraint conditions, wherein the lower layer constraint conditions comprise alternating current line power flow transmission constraint and lower layer load shedding constraint;
the lower layer objective function is the minimum load shedding quantity:
wherein, betaqAn important coefficient representing the load of class q,. DELTA.PLSt,d,qRespectively representing q-type load quantities cut off by the node d in a t period;
the alternating current line power flow transmission constraint is as follows:
wherein, SF (-) represents a power flow transfer expression, PG represents a matrix vector of the output of the synchronous unit i in the t-th time period, PW represents a matrix vector of the output of the wind turbine j in the t-th time period, PHC represents a matrix vector of the transmission power of the fault direct current line l before locking, Δ PHC represents a matrix vector of the modulation power of the h-th non-fault direct current in the t-th time period, PD represents a matrix vector of the active demand of the load d in the t-th time period,
a matrix vector representing an optimal derating amount of the lower model;
the lower shear load constraint is as follows:
where ζ represents the load shedding ratio, and q represents the number of types of loads.
The method for respectively carrying out iterative solution on the upper layer model and the lower layer model by utilizing the target cascade analysis method to obtain the maximum direct current feed-in quantity of the receiving-end power grid comprises the following steps:
s51: initializing a coupling variable and a penalty function multiplier, and setting the iteration number k to be 1;
s52: solving the lower layer model by utilizing a solver carried by the GAMS platform according to the lower layer objective function and the lower layer constraint condition to obtain the optimal load shedding amount
And the optimal load shedding amount is obtained
Transferring to an upper model;
s53: the upper layer model receives the optimal load reduction amount transmitted by the lower layer model
Then, solving the upper model by using a solver carried by the GAMS platform according to an upper objective function and an upper constraint condition to obtain load shedding quantity delta PLStTransmitting to the lower model;
s54: determining load shedding quantity Delta PLS of k iterationstAnd optimum load shedding amount
And if the convergence condition is met, terminating the iteration process and outputting the maximum direct current feed-in amount of the receiving-end power grid, otherwise, updating the penalty function multiplier, and returning to the step S52 if the iteration number k is k + 1.
The convergence condition is as follows:
wherein the content of the first and second substances,
representing the amount of load shedding at k-1 iterations,
represents the optimal derating amount, θ, at k-1 iterations1、θ2Both indicate the allowable error in the sense that,
representing variable PHCt,hThe value in the k-th iteration,
representing variable PHCt,hValues in the k-1 th iteration.
The method for updating the penalty function multiplier comprises the following steps:
γk＝μγk-1，
wherein alpha isk、γkAll represent a penalty factor, α, for k iterationsk-1、γk-1All represent the penalty coefficient in k-1 iterations, mu is a constant,
representing the amount of load shedding at k-1 iterations,
representing the optimal amount of reduction at k-1 iterations.
The beneficial effect that this technical scheme can produce:
(1) aiming at the problems of power shortage and rapid frequency reduction of a receiving-end power grid caused by high-capacity direct current blocking, in order to avoid the third line-defense-low-frequency load shedding action of the system, the primary frequency modulation direct current emergency power support and accurate load shedding of the system are coordinated, and the conservative degree of the ultimate transmission power of the direct current connecting line obtained through evaluation is reduced;
(2) the constraint conditions of the upper layer model and the lower layer model constructed by the invention are based on the actual operation of the power grid and combined with the basic theory of the power system, and specifically comprise the following steps: 1) in the aspect of receiving-end power grid operation constraint, standby requirements of a single unit and the whole receiving-end power grid are considered in combination with the system primary frequency modulation after the fault, and power balance constraint and power flow constraint are considered in combination with the normal operation state of the receiving-end power grid; 2) in the aspect of direct current tie line power constraint, a series of related constraints are constructed aiming at the limitation that the tie line power has to operate in a certain numerical value within the minimum time and the all-weather operation times are required by actual scheduling; by modeling the upper layer model and the lower layer model, the calculation result of the method is closer to the practical operation of the receiving-end power grid;
(3) according to the invention, the lower-layer model is constructed to ensure that when a direct-current bipolar blocking fault occurs, the load cut by a receiving-end power grid is minimum, and the benefit of a power consumer is ensured to the greatest extent;
(4) the GAMS platform is used for modeling and calling the solver to solve, and the whole solving process is simple, quick and effective.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a circuit diagram of an improved RTS79 system of the invention;
FIG. 2 is a comparison of transmission power at each time interval for three DC links;
FIG. 3 shows the frequency offset after a DC blocking fault at time interval 7 according to the present invention;
FIG. 4 shows the frequency offset after a DC blocking fault in time interval 7 in the TTC method;
FIG. 5 is a flow chart of the present invention.
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 only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
As shown in fig. 5, an embodiment of the present invention provides a receiving-end power grid dc maximum feed-in amount evaluation method based on target cascade analysis, which includes the following specific steps:
s1: analyzing the sensitivity of different types of loads of adjacent bus nodes of a fault point to frequency recovery of a receiving-end power grid system, and dividing the loads into high-sensitivity loads and low-sensitivity loads; FIG. 1 is a circuit diagram of an improved RTS79 system with wind turbines at bus nodes s214, s207, respectively, via h connected at bus nodes s203, s217, and s223, respectively1、h2And h3The three HVDC lines externally transmit electric power, and the transmission capacities of the three HVDC lines are 500MW, 600MW and 750MW respectively. DC link (h) with maximum capacity to be considered in the DC maximum transmission capability assessment method3) The system can still maintain the frequency stability of the system under the bipolar lockout fault (the action of a high-frequency generator tripping device is not triggered). When a large-capacity direct-current bipolar latching fault occurs in a large-capacity direct-current communication line, acquiring the frequency characteristic of a receiving-end power grid, wherein the frequency characteristic of the receiving-end power grid is a change mechanism of the frequency characteristic of the receiving-end power grid on a time scale; for a system with a specific structure and a fault condition, the sensitivity characterization of the removal of different loads on the frequency recovery of the system after the fault is different, and some loads are sensitive and some loads are insensitive. Therefore, when load shedding is performed, if a load having high sensitivity to system frequency recovery is first shed, frequency recovery can be achieved by only shedding a relatively small amount of load. The invention adopts a simulation experiment method to determine the load removal of the adjacent nodes of the fault point and the frequency recovery and fluctuation of the systemSensitivity relationship. The specific method comprises the following steps:
s11: setting that the sensitivity of the system to frequency recovery and fluctuation is the same when all loads of adjacent bus nodes of a fault point are removed so as to ensure that the initial state before removal is consistent;
s12: setting an expected accident set which comprises r typical faults, and acquiring a frequency curve f' of the system after the load corresponding to the fault p is removed by using electromechanical simulation software BPA; the system comprises a fault detection circuit, a fault control circuit and a fault control circuit, wherein typical faults comprise a three-phase short circuit, a single-phase short circuit, a two-phase grounding short circuit, a direct current single-pole lock, a direct current double-pole lock and a generator set trip, the fault p is the generator set trip, and the capacity is 6000 MW;
s13: for the same fault p, cutting off the load with the same capacity as the synchronous generator set corresponding to the same fault p on the adjacent node of the same fault p, and acquiring a frequency curve f' of the system by using electromechanical simulation software;
s14: respectively carrying out equally-spaced discrete processing on the frequency curves f ' and f ' and calculating the offset coefficients alpha ' of adjacent nodes with the same fault p:
wherein n 'is an interval, n' is 1,2, …, 3000;
s15: calculating the average offset coefficient alpha 'of each adjacent node load to the forecast accident set respectively'aveAnd shifting the average shift coefficient by α'aveAs the sensitivity of the corresponding load shedding to the frequency recovery and the fluctuation, the larger the average offset coefficient is, the better the system frequency recovery is, and the higher the sensitivity of the load shedding of the node to the frequency recovery and the fluctuation is. Coefficient of offset α 'from magnitude to average'aveAnd sorting is carried out, and the loads of the nodes adjacent to the fault point are divided into high-sensitivity loads and low-sensitivity loads according to the divided threshold (the threshold is 0.4).
S2: acquiring a low-frequency suppression strategy of the receiving-end power grid after the high-capacity direct-current bipolar blocking fault according to the frequency characteristic of the receiving-end power grid; combining a swing equation of a receiving-end power grid, and acquiring a frequency stability control strategy of the receiving-end power grid after a high-capacity direct-current bipolar blocking fault according to the frequency characteristic of the receiving-end power grid; the low-frequency suppression strategy is a coordination strategy of primary frequency modulation, direct current modulation and accurate load shedding, and when a bipolar locking fault occurs in high-capacity direct current, a large amount of power shortage occurs in a receiving-end power grid, so that the system frequency is sharply reduced. In order to ensure the quick recovery of the system frequency and avoid the low-frequency load shedding action of the third defense line, the first defense line (primary frequency modulation) and the second defense line (load shedding and direct current modulation) must act cooperatively to inhibit the instability of the system frequency. After the fault happens, the primary frequency modulation reserve of the receiving end power grid must be matched with direct current modulation and load shedding, the frequency of the system is restrained from dropping too fast, the RoCoF relay protection and low-frequency load shedding device of the system are prevented from being triggered, and the specific strategy is as follows:
s21: at the moment of failure, the direct current emergency power supports rapid action, and part of blocking power of the failed direct current is transferred to a non-failed direct current connecting line; meanwhile, the load shedding device acts, and the unbalanced power of the system is reduced as follows:
wherein the content of the first and second substances,
indicates the unbalanced power of the transmission network at the moment of bipolar latch-up occurrence,. DELTA.PL'tShowing the unbalanced power after the DC modulation and load shedding action of the system, wherein Δ PLS is the total load after fault shedding, and Δ PHChThe modulation quantity of the h-th non-fault direct current is obtained;
the direct current power modulation amount and the load shedding amount meet the following constraint conditions:
wherein the content of the first and second substances,
represents the upper limit value of the transmission power of the h-th non-fault direct current,
representing the maximum emergency modulation amount of the h-th non-fault direct current, wherein rho represents the overload proportion allowed by short-term direct current modulation, and the value of rho does not exceed 10% generally;
s22: the transmission power of the h-th non-fault dc participating in emergency power support is kept at a constant value PHC during the primary fm response time (typically 30s)h+△PHCh；
S23: when the frequency deviation of the system exceeds the dead zone of the frequency of the generator, all synchronous generator sets participating in primary frequency modulation gradually release rotation for standby application to increase output force, so that the unbalanced power of the system is further reduced until the frequency of the system reaches a quasi-steady state.
S3: constructing an upper layer model according to the low-frequency suppression strategy in the step S2; the method is characterized in that the method takes the maximization of the direct current feed-in quantity of a receiving-end power grid as a target, and takes the frequency stability constraint of the receiving-end power grid, the operation constraint of the receiving-end power grid and the power constraint of a direct current tie line as constraint conditions. Upper layer model to receive optimal derating amount from lower layer model
Calculating the maximum DC feed for the parameters and applying the corresponding load shedding quantity Δ PLStAnd sending the data to the lower layer model. The upper layer model comprises an upper layer objective function and upper layer constraint conditions, wherein the upper layer constraint conditions comprise a receiving end power grid frequency stability constraint, a receiving end power grid operation constraint, a direct current tie line power constraint and an upper layer load shedding constraint;
the upper-layer objective function is to maximize the direct current feed-in quantity of a receiving-end power grid:
wherein, TTCtRepresenting transmission power, alpha, of period tt、γtAll represent a penalty factor,. DELTA.PLStThe amount of the load to be cut is shown,
representing the optimal load reduction amount of the lower model;
the receiving end power grid frequency stabilization comprises extreme value frequency constraint and frequency change rate constraint;
the constrained frequency rate of change constraint is:
wherein the content of the first and second substances,
indicates an unbalanced power, delta PL ', of the transmission-side power grid at the moment of occurrence of bipolar latch-up'tShows the unbalanced power after the system DC modulation and load shedding action, RoCoFtIndicates the frequency change rate of the transmitting end power grid in the t period, delta PGTtRepresenting the load shedding quantity, PHC, of the transmission-end power grid in the period tt,lIndicating the transmission power of the faulty DC line l before blocking, RoCoFmaxRepresents a tolerable maximum value of the rate of change of frequency; htRepresenting the level of inertia of the system during the period t,
representing the maximum output, f, allowed by the synchronous unit i0System frequency, H, representing the moment of failureiRepresenting the inertia level, Δ PLS, of the synchronous set itIndicates the total cutter amount, Δ PHC, of the t periodt,hRespectively representing the modulation power of the h-th non-fault direct current in the t period; the equation (6) strictly limits the initial frequency change rate after the fault, and it can be seen that the initial frequency change rate is inversely proportional to the inertia level number of the system and is directly proportional to the magnitude of the unbalanced power; calculating the inertia level of the system by formula (7); formula (8) represents the initial power unbalance of the system after the direct current tie line l is locked; equation (9) represents the amount of power imbalance after the corrective control action (dc modulation, load shedding).
The extreme frequency constraint is:
wherein rr isiRepresenting the climbing rate of the synchronous unit i; f. ofminRepresenting the low-frequency deloading operating frequency, f, of the receiving-end griddbThe frequency dead zone of a receiving-end power grid is shown, and the delta PLS is the total load after the fault is removed;
representing a primary frequency modulation up-regulation standby value of a synchronous unit i in a scene u at a time period t; the formula (10) is obtained by combining the formula (9), the formula (11) and the formula (12);
constraint (11) ensures that each unit releases the frequency to be adjusted for standby once before the system reaches a frequency extreme value; constraints (12) ensure that the primary frequency modulation reserve of all synchronous units is sufficient to counteract the system power after action of corrective control measuresUnbalance amount delta PL't。
The receiving end power grid operation constraint comprises active power balance constraint, transmission power constraint of a power transmission line, unit output/climbing constraint, rotation standby constraint and normal state operation constraint;
the active power balance constraint is:
wherein PGt,i,uRepresents the output, PW, of the synchronous unit i in the t period under the scene ut,j,uRepresents the output, PD, of the wind turbine set j in the time period t under the scene ut,dRepresenting the active demand, PHC, of load d during time tt,hRepresenting the transmission power of the h-th non-fault direct current in a t period;
the transmission power constraint of the transmission line is as follows:
wherein, SFb,nRepresenting the power transfer factor, KGb,iIndicating node association factor, KW, of synchronous setsb,jRepresenting the node association factor, KD, of the wind turbineb,dA node association factor representing the load,
representing the maximum transmission capacity allowed by the nth AC line in the receiving end power grid; the constraint (14) ensures that the internal circuit of the receiving end power grid does not have the out-of-limit tidal current under the normal condition.
The unit output/climbing constraints are:
wherein the content of the first and second substances,
represents the maximum output allowed by the wind turbine j,
represents the minimum output allowed by the synchronous unit i,
represents the maximum output allowed by the synchronization unit i,
indicating a ramp down limit for the synchronous unit i,
indicating the uphill limit of the synchronized group i,
representing the primary frequency modulation up-regulation standby value of a synchronization unit i in the t-th time period under a scene u;
presentation fieldJingu2The output of the lower synchronous unit i in the t-th time period,
representing a scene u3The output of the lower synchronous unit i in the t-th time period,
representing a scene u2The output of the lower synchronous machine set i in the t-1 th time period,
respectively representing a presentation scene u3The output of the lower synchronous unit i in the t-th time period; calculating the transmission power of each direct current line in a single time period by using a formula (15); formulas (16) - (17) ensure that the output of the synchronous generator set and the wind generator set is not out of limit; the formula (18) ensures that the output of the unit at the adjacent small time meets the climbing limitation, and the formulas (19) and (20) show that the output of the unit at the adjacent small time needs to meet the limit scene (the upper bound u of the wind power output)2Lower bound u of wind power output3) And (5) limiting the downward climbing.
The rotational standby constraints are:
wherein the content of the first and second substances,
representing the maximum value of the primary frequency modulation up-regulation reserve of the synchronous unit i;
the normal state operating constraints are:
wherein the content of the first and second substances,
represents the minimum transmission power of the h-th non-faulty dc,
representing the maximum transmission power of the h-th non-fault direct current; constraints (22) ensure that the normal state dc lines operate within a reasonable range.
The direct current tie line power constraint comprises a direct current power adjustment stepped constraint, an adjacent time interval non-backward adjustment constraint, a direct current tie line all-day adjustment frequency constraint and a direct current tie line emergency power support constraint;
the step constraint of the direct current power adjustment is as follows:
wherein, Δ PHCt,hThe power adjustment quantity of the h non-fault direct current in the t period after the fault occurs is shown,
a limit value representing the h-th non-faulted dc single-trip down-regulation,
a limit value representing the h-th non-faulted dc one-time up-adjustment amount,
indicating the rising edge of the power adjustment step for the h-th non-failing dc during the t period,
indicating the falling edge of the power adjustment step of the h-th non-fault dc during the period t,
and
is a variable of 0 to 1, It,hIndicating the operating state of the h-th non-fault DC in the period t, It-1,hIndicating the operation state of the h-th non-fault direct current in the t-1 period,
the shortest continuous operation time of the h-th non-fault direct current at a certain power level is represented; through the coordination of the formulas (23) - (26), the operation requirement that the stepped modulation only occurs when the power of the direct current connecting line meets the shortest duration is realized.
The adjacent time period must not be adjusted reversely and is constrained as follows:
wherein the content of the first and second substances,
indicating the rising edge of the power adjustment step for the h-th non-failing dc during the t-1 period,
the power adjustment step of the h-th non-fault direct current in the t-1 period is shown;
the constraint of the whole-day adjustment times of the direct current tie line is as follows:
wherein phi ish6 represents the upper limit of the h-th non-fault direct current all-day regulation times, and T24 represents the total time interval number;
after the dc bipolar latch occurs in any time period t, the dc link emergency power support constraint is:
wherein, rho represents the overload ratio allowed by the short-term direct current modulation; constraint (30) indicates that the non-fault direct current line can be operated in an overload mode for a period of time after fault, and the overload rate rho is 10%; while the constraint (31) requires that the adjustment of the non-faulty lines participating in the dc emergency power support does not exceed a maximum reasonable value.
The upper layer shear load constraint is as follows:
△PLSt≤△PLSmax (32)。
s4: constructing a lower layer model according to the high sensitivity load and the low sensitivity load in the step S1; aiming at the minimum load shedding, taking alternating current line power flow transmission constraint and lower layer load shedding constraint as constraint conditions; the lower model is based on the tangential load quantity Δ PLS received from the upper modeltAnd the penalty coefficients alpha and gamma coordinate and optimize the load shedding amount of each target node, and update and upload the load shedding amount to an upper layer model. The lower layer model comprises a lower layer objective function and lower layer constraint conditions, wherein the lower layer constraint conditions comprise alternating current line power flow transmission constraint and lower layer load shedding constraint;
the lower layer objective function is the minimum load shedding amount:
wherein, betaqImportant coefficient representing class q load,. DELTA.PLSt,d,qRespectively representing q-type load quantities cut off by the node d in a t period;
the alternating current line power flow transmission constraint is as follows:
wherein, SF (-) represents a power flow transfer expression, PG represents a matrix vector of the output of the synchronous unit i in the t-th time period, PW represents a matrix vector of the output of the wind turbine j in the t-th time period, PHC represents a matrix vector of the transmission power of the fault direct current line l before locking, Δ PHC represents a matrix vector of the modulation power of the h-th non-fault direct current in the t-th time period, PD represents a matrix vector of the active demand of the load d in the t-th time period,
a matrix vector representing an optimal derating amount of the lower model; the constraint (34) ensures that the alternating current line power flow does not exceed the limit after the action of the stable control load shedding measure.
The lower shear load constraint is as follows:
where ζ represents a load shedding ratio, and q represents the number of categories of the load; the constraint (35) calculates the load shedding amount of a single time interval; constraints (36) - (37) ensure that the individual node's load shedding and the total load shedding are within reasonable ranges.
S5: respectively carrying out iterative solution on the upper layer model and the lower layer model by using a target cascade analysis method to obtain the maximum direct-current feed-in quantity of the receiving-end power grid; respectively modeling an upper layer model and a lower layer model by using a GAMS platform, calling a solver carried by the GAMS platform, inputting a unit state/upper output limit, transmission upper and lower limits/adjustment limits of a direct current connection line, upper and lower limits and direct current connection line full-day adjustment maximum times of system rotation, using unit up/down regulation standby, direct current modulation quantity, load shedding quantity and all direct current transmission power as decision variables, using the total load shedding quantity as a shared variable, carrying out iterative solution by using a target cascade analysis method, judging whether iteration is finished according to convergence conditions, and obtaining the maximum receiving-end power grid direct current feed-in quantity. The specific method comprises the following steps:
s51: initializing a coupling variable (total load shedding amount) and a penalty function multiplier (an initial value is 0), and setting the iteration number k to be 1;
s52: solving the lower layer model by utilizing a solver (miqcp) of the GAMS platform according to the lower layer objective function and the lower layer constraint condition to obtain the optimal load shedding amount
And the optimal load shedding amount is obtained
Transferring to an upper model;
s53: the upper layer model receives the optimal load reduction amount transmitted by the lower layer model
Then, solving the upper model by using a solver carried by the GAMS platform according to an upper objective function and an upper constraint condition to obtain load shedding quantity delta PLStTransmitting to the lower model;
s54: determining load shedding quantity Delta PLS of k iterationstAnd optimum load shedding amount
If the convergence condition is met, terminating the iterative process and outputting the maximum direct current feed-in quantity of the receiving-end power grid if the convergence condition is met, otherwise, updating the penalty functionWith the multiplier, the number of iterations k is k +1, and the process returns to step S52.
The convergence condition is as follows:
wherein the content of the first and second substances,
representing the amount of load shedding at k-1 iterations,
represents the optimal derating amount, θ, at k-1 iterations1、θ2Both indicate the allowable error in the sense that,
representing variable PHCt,hThe value in the k-th iteration,
representing variable PHCt,hValues in the k-1 th iteration.
The method for updating the penalty function multiplier comprises the following steps:
γk＝μγk-1 (41)，
wherein alpha isk、γkAll represent a penalty factor, α, for k iterationsk-1、γk-1All represent the penalty coefficient in k-1 iterations, mu is a constant,
representing the amount of load shedding at k-1 iterations,
represents the optimal derating amount at k-1 iterations; mu is 2<μ<And 3, the initial value of alpha is 1.2, and the initial value of gamma is 1.35.
Fig. 2 compares the transmission power of 3 direct currents in each time interval in the method (FTTC) of the present invention with the conventional TTC model method (frequency stability is considered and not considered). Wherein, h is the FTTC model1、h2Near full load operation. Comparing TTC model with h in FTTC model3Is smaller at times t1-t10, which means when h is greater than h3When bipolar latching faults occur in the time periods, the receiving-end power grid is prone to frequency instability. In addition, the power curves of the three direct current connecting lines have good step performance, the power adjustment times are less than 6, and the operation of an actual power grid is met.
Fig. 3 and 4 illustrate the frequency offset situation after the slot 7 dc blocking fault in the FTTC method and the frequency offset situation after the slot 7 dc blocking fault in the TTC method, respectively. For the TTC model, the frequency stability is not considered at h3The system frequency collapses after bipolar latching, which triggers a low frequency load shedding action of the system. On the contrary, because the FTTC model considers the frequency stability, the system frequency can be timely restored to a reasonable quasi-steady-state frequency after the fault.
By adopting the method to evaluate the maximum direct current feed-in amount of the receiving-end power grid, the conservative degree of the calculation result is lower because: compared with the traditional method only considering a single direct current modulation strategy or an accurate load shedding strategy, the method aims at the problems of power shortage and rapid frequency reduction of a receiving end power grid caused by high-capacity direct current blocking, and in order to avoid the third line of defense-low frequency load shedding action of the system, the method considers the coordination and cooperation of the primary frequency modulation direct current emergency power support and the accurate load shedding action of the system, so that the ultimate transmission power of the direct current connecting line obtained through evaluation is not conservative.
By adopting the method of the invention to evaluate the maximum direct current feed-in quantity of the receiving-end power grid, the calculation result is more in line with the actual operation of the power grid, and the reason is that: the construction of the constraint conditions of the upper layer model and the lower layer model is based on the actual operation of the power grid and combines the basic theory of the power system. The concrete body is as follows: 1) in the aspect of receiving-end power grid operation constraint, standby requirements of a single unit and the whole receiving-end power grid are considered in combination with the system primary frequency modulation after the fault, and power balance constraint and power flow constraint are considered in combination with the normal operation state of the receiving-end power grid; 2) in the aspect of direct current tie line power constraint, a series of related constraints are constructed aiming at the limitation that the tie line power has to operate in a certain numerical value within the minimum time and the all-weather operation times are required by actual scheduling. Through the modeling, the calculation result of the method is closer to the practical operation of the receiving-end power grid.
By adopting the method disclosed by the invention, the maximum direct-current feed-in quantity of the receiving-end power grid is evaluated, and the calculation result can ensure that the load cut by the receiving-end power grid is minimum when the direct-current bipolar latching fault occurs by constructing the lower-layer model, so that the benefit of a power consumer is ensured to the maximum extent.
The method for evaluating the maximum direct-current feed-in quantity of the receiving-end power grid based on the cascade analysis is easy to model by using a GAMS platform and call a solver to solve, and the whole solving process is simple, quick and effective.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. A receiving-end power grid direct-current maximum feed-in quantity evaluation method based on target cascade analysis is characterized by comprising the following steps:
s1: analyzing the sensitivity of different types of load removal of the adjacent bus nodes of the fault point to the frequency recovery of the receiving-end power grid system, and dividing the load into a high-sensitivity load and a low-sensitivity load;
s2: acquiring a low-frequency suppression strategy of a receiving-end power grid after a high-capacity direct-current bipolar blocking fault according to the frequency characteristic of a receiving-end power grid system;
s3: constructing an upper layer model according to the low-frequency suppression strategy in the step S2;
s4: constructing a lower layer model according to the high sensitivity load and the low sensitivity load in the step S1;
s5: and respectively carrying out iterative solution on the upper layer model and the lower layer model by using a target cascade analysis method to obtain the maximum direct-current feed-in quantity of the receiving-end power grid.
2. The receiving-end power grid direct-current maximum feed-in quantity evaluation method based on target cascade analysis according to claim 1, wherein the method for analyzing the sensitivities of different load removal of the bus nodes adjacent to the fault point to system frequency recovery is as follows:
s11: setting that the sensitivity of the system to frequency recovery and fluctuation is the same when all loads of adjacent bus nodes of a fault point are removed;
s12: setting an expected accident set which comprises r typical faults, and acquiring a frequency curve f' of the system after the load corresponding to the fault p is removed by using electromechanical simulation software BPA, wherein the typical faults comprise a three-phase short circuit, a single-phase short circuit, a two-phase grounding short circuit, a direct-current single-pole latch, a direct-current double-pole latch and a generator set trip;
s13: for the same fault p, cutting off the load with the same capacity as the synchronous generator set corresponding to the same fault p on the adjacent node of the same fault p, and acquiring a frequency curve f' of the system by using electromechanical simulation software;
s14: respectively carrying out equally-spaced discrete processing on the frequency curves f 'and f' and calculating the offset coefficient alpha of the adjacent nodes with the same fault p:
wherein n 'is an interval, n' is 1,2, …, 3000;
s15: respectively calculating the average deviation coefficient alpha of the loads of the adjacent nodes to the expected accident setaveAnd by the magnitude to average offset coefficient alphaaveSorting, and dividing the fault by the set dividing thresholdThe point-adjacent node load is divided into a high-sensitivity load and a low-sensitivity load.
3. The target cascade analysis-based receiving-end power grid direct-current maximum feed-in amount evaluation method according to claim 1, wherein the low-frequency suppression strategy is a coordination strategy of primary frequency modulation, direct-current modulation and accurate load shedding, and the specific strategy is as follows:
s21: at the moment of failure, the direct current emergency power supports rapid action, and part of blocking power of the failed direct current is transferred to a non-failed direct current connecting line; meanwhile, the load shedding device acts, and the unbalanced power of the system is reduced as follows:
wherein, Δ PL0Showing the unbalanced power of a sending-end power grid at the moment of bipolar latch-up, showing the unbalanced power after system direct current modulation and load shedding action by delta PL', showing the total load quantity after fault removal by delta PLS and showing the total load quantity after fault removal by delta PHChThe modulation quantity of the h-th non-fault direct current line is obtained, h is the non-fault direct current line, and l is the fault direct current line;
the constraint conditions met by the direct current power modulation quantity are as follows:
the load shedding amount satisfies the constraint conditions:
wherein the content of the first and second substances,
represents the transmission power upper limit value of the h-th non-faulty direct-current line,
the maximum emergency modulation amount of the h-th non-fault direct-current line is represented, and rho represents the overload proportion allowed by short-term direct-current modulation;
s22: the transmission power of the h-th non-faulty DC line participating in emergency power support is maintained at a constant value PHC during the primary FM response timeh+△PHCh；
S23: when the frequency deviation of the system exceeds the dead zone of the frequency of the generator, all synchronous generator sets participating in primary frequency modulation gradually release rotation for standby application to increase output force, so that the unbalanced power of the system is reduced until the frequency of the system reaches a quasi-steady state.
4. The method for evaluating the maximum direct-current feed-in quantity of the receiving-end power grid based on the target cascade analysis according to claim 1, wherein the upper-layer model comprises an upper-layer objective function and upper-layer constraint conditions, and the upper-layer constraint conditions comprise a receiving-end power grid frequency stability constraint, a receiving-end power grid operation constraint, a direct-current tie line power constraint and an upper-layer load shedding constraint;
the upper-layer objective function is to maximize the direct current feed-in quantity of a receiving-end power grid:
wherein, TTCtRepresenting transmission power, alpha, of period tt、γtAll represent a penalty factor,. DELTA.PLStThe amount of the load to be cut is shown,
representing the optimal load reduction amount of the lower model, wherein t is a time period;
the receiving end power grid frequency stability constraint comprises a frequency change rate constraint and an extreme value frequency constraint;
the frequency rate constraint is:
wherein the content of the first and second substances,
representing the unbalanced power, RoCoF, after system DC modulation and load shedding actiontRepresenting the rate of change of frequency of the sending-end grid during time t,
representing the inertia level of the system during the t period, RoCoFmaxRepresents a tolerable maximum value of the rate of change of frequency,
PHC representing the instantaneous unbalanced power of the transmitting grid at the moment of bipolar blockingt,lThe transmission power of the fault direct-current line l before locking is represented;
representing the maximum output, f, allowed by the synchronous unit i0System frequency, H, representing the moment of failureiRepresenting the inertia level, Δ PLS, of the synchronous unit itIndicates the total cutter amount, Δ PHC, of the t periodt,hRespectively representing the modulation power of the h-th non-fault direct-current line in the t period;
the extreme frequency constraint is:
wherein rr isiRepresenting the climbing rate of the synchronous unit i; f. ofminRepresenting the low-frequency deloading operating frequency, f, of the receiving-end griddbThe frequency dead zone of a receiving-end power grid is shown, and the delta PLS is the total load after the fault is removed;
represents under scene uA synchronous unit i adjusts a standby value in primary frequency modulation at a time period t;
the receiving end power grid operation constraint comprises active power balance constraint, transmission power constraint of a power transmission line, unit output/climbing constraint, rotation standby constraint and normal state operation constraint;
the active power balance constraint is:
wherein PGt,i,uRepresents the output, PW, of the synchronous unit i in the t period under the scene ut,j,uRepresents the output, PD, of the wind turbine set j in the t period under the scene ut,dRepresents the active demand of the load d in the period t, PHCt,hRepresenting the transmission power of the h-th non-fault direct current line in a t period;
the transmission power constraint of the transmission line is as follows:
wherein, SFb,nRepresenting the power transfer factor, KGb,iIndicating node association factor, KW, of synchronous setsb,jRepresenting the node association factor, KD, of the wind turbineb,dA node association factor representing the load,
representing the maximum transmission capacity allowed by the nth AC line in the receiving end power grid;
the unit output/climbing constraints are:
-RPi dn≤PGt,i,u-PGt-1,i,u≤RPi up，
wherein the content of the first and second substances,
represents the maximum output allowed by the wind turbine j,
represents the minimum output allowed by the synchronous unit i,
indicating the maximum allowable output, RP, of the synchronous unit ii dnIndicating a downward hill climb restriction, RP, of the synchronous unit ii upIndicating the uphill limit of the synchronized group i,
indicating that the synchronous unit i in the scene u adjusts the standby value in the primary frequency modulation of the t-th time period,
representing a scene u2The output of the lower synchronous unit i in the t-th time period,
representing a scene u3The output of the lower synchronous machine set i in the t-1 th time period,
representing a scene u2The output of the lower synchronous machine set i in the t-1 th time period,
representing a scene u3The output of the lower synchronous unit i in the t-th time period;
the rotational standby constraints are:
wherein, Pi ru,maxRepresenting the maximum value of the primary frequency modulation up-regulation reserve of the synchronous unit i;
the normal state operating constraints are:
wherein the content of the first and second substances,
indicates the minimum transmission power of the h-th non-faulty dc line,
representing the maximum transmission power of the h-th non-fault direct current line;
the direct current tie line power constraint comprises a direct current power adjustment stepped constraint, an adjacent time interval non-reversible adjustment constraint, a direct current tie line all-day adjustment frequency constraint and a direct current tie line emergency power support constraint;
the step constraint of the direct current power adjustment is as follows:
wherein, Δ PHCt,hThe power adjustment quantity of the h-th non-fault direct current line in the t period after the fault occurs is shown,
a limit value representing a single down adjustment of the h-th non-faulted dc line,
a limit value representing a single upward adjustment of the h-th non-faulted dc link,
indicating the rising edge of the power adjustment step of the h-th non-faulty dc line during the period t,
indicating the falling edge of the power adjustment step of the h-th non-fault direct current line in the period t, It,hRepresenting the operating state of the h-th non-faulty DC line during a time period t, It-1,hIndicating the operation state of the h-th non-fault direct current line in the t-1 period,
the shortest continuous operation time of the h-th non-fault direct-current line at a certain power level is represented;
the adjacent time period must not be adjusted reversely and is constrained as follows:
wherein the content of the first and second substances,
indicating the rising edge of the power adjustment step of the h-th non-faulty dc line during the period t-1,
the method comprises the steps of representing the falling edge of a power adjustment step of the h-th non-fault direct-current line in a t-1 period;
the constraint of the all-day adjustment times of the direct current connecting line is as follows:
wherein phi ishRepresenting the total day adjustment frequency upper limit of the h-th non-fault direct-current line, wherein T represents the total time interval quantity;
the direct current tie line emergency power support constraints are:
wherein, rho represents the overload ratio allowed by the short-term direct current modulation;
the upper layer shear load constraint is as follows:
△PLSt≤△PLSmax。
5. the target cascade analysis-based receiving-end grid direct-current maximum feed-in quantity evaluation method according to claim 4, wherein the lower layer model comprises a lower layer objective function and lower layer constraint conditions, and the lower layer constraint conditions comprise an alternating current line power flow transmission constraint and a lower layer load shedding constraint;
the lower layer objective function is the minimum load shedding amount:
wherein, betaqImportant coefficient representing class q load,. DELTA.PLSt,d,qRepresenting the q-type load amount cut off by the node d in the t period;
the alternating current line power flow transmission constraint is as follows:
wherein, SF (-) represents a power flow transfer expression, PG represents a matrix vector of the output of the synchronous unit i in the t-th time period, PW represents a matrix vector of the output of the wind turbine j in the t-th time period, PHC represents a matrix vector of the transmission power of the fault direct current line l before locking, Δ PHC represents a matrix vector of the modulation power of the h-th non-fault direct current line in the t-th time period, PD represents a matrix vector of the active demand of the load d in the t-th time period,
a matrix vector representing an optimal derating amount of the lower model;
the lower shear load constraint is as follows:
where ζ represents the load shedding ratio, and q represents the number of types of loads.
6. The method for evaluating the maximum direct-current feed-in quantity of the receiving-end power grid based on the target cascade analysis according to claim 1, wherein the target cascade analysis method is used for respectively carrying out iterative solution on the upper layer model and the lower layer model, and the method for obtaining the maximum direct-current feed-in quantity of the receiving-end power grid is as follows:
s51: initializing a coupling variable and a penalty function multiplier, and setting the iteration number k to be 1;
s52: solving the lower layer model by utilizing a solver carried by the GAMS platform according to the lower layer objective function and the lower layer constraint condition to obtain the optimal load shedding amount
And the optimal load shedding amount is obtained
Transferring to an upper model;
s53: the upper layer model receives the optimal load reduction amount transmitted by the lower layer model
Then, solving the upper model by using a solver carried by the GAMS platform according to an upper objective function and an upper constraint condition to obtain load shedding quantity delta PLStTransmitting to the lower model;
s54: determining load shedding quantity Delta PLS of k iterationstAnd optimum load shedding amount
And if the convergence condition is met, terminating the iteration process and outputting the maximum direct current feed-in amount of the receiving-end power grid, otherwise, updating the penalty function multiplier, and returning to the step S52 if the iteration number k is k + 1.
7. The method for evaluating the maximum direct-current feed-in amount of the receiving-end power grid based on the target cascade analysis according to claim 6, wherein the convergence condition is as follows:
wherein the content of the first and second substances,
representing the amount of load shedding at k-1 iterations,
represents the optimal derating amount, θ, at k-1 iterations1、θ2Both of which represent an allowable error, and,
representing variable PHCt,hThe value in the k-th iteration,
representing variable PHCt,hThe value in the k-1 iteration; t represents a time period; h denotes a non-faulty dc line.
8. The receiving-end grid direct-current maximum feed-in amount evaluation method based on target cascade analysis according to claim 6, wherein the method for updating penalty function multipliers is as follows:
γk＝μγk-1，
wherein alpha isk、γkAll represent a penalty factor, α, for k iterationsk-1、γk-1All represent the penalty coefficient in k-1 iterations, mu is a constant,
representing the amount of load shedding at k-1 iterations,
representing the optimal amount of reduction at k-1 iterations.
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| CN108599223A (en) * | 2018-05-04 | 2018-09-28 | 华北电力大学 | The method of extra-high voltage direct-current receiving end power grid emergent control and Corrective control on-line decision |
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