A security-constrained optimal power flow control method and system for an ac-dc hybrid power grid

Abstract

The application provides a security-constrained optimal power flow control method and system for an AC-DC hybrid power grid, comprising the following steps: inputting the operation data of generators, AC buses and DC nodes in the AC-DC hybrid power grid into a pre-established preventive correction control security-constrained optimal power flow model to obtain optimal rescheduling amounts of generator outputs and optimal rescheduling amounts of loads; and adjusting the generator outputs and load consumptions according to the optimal rescheduling amounts of the generator outputs and the optimal rescheduling amounts of the loads. Compared with the prior art, the method and system have the following significant features: the preventive control security-constrained optimal power flow is combined with the correction control security-constrained optimal power flow, and is applied to the AC-DC hybrid power grid, so that the optimal decision of the AC-DC hybrid power grid considering the economy and reliability is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of AC / DC power transmission system, and particularly relates to a security constrained optimal power flow control method and system for an AC / DC hybrid power grid. BACKGROUND

[0002] In recent years, high voltage direct current (HVDC) technology has gradually developed, has been widely applied to modern power grids to realize long-distance transmission of large-capacity electric energy, and gradually forms a safe and stable AC / DC power grid, but how to realize safe and economic optimal operation has become one of the key topics of researchers at home and abroad.

[0003] Security constrained optimal power flow (SCOPF) is an optimal power flow model considering the security operation constraint under the expected accident, and is an important dispatching method for realizing safe and reliable operation of a power system. The existing security constrained optimal power flow only adjusts the operating point to meet the security operation constraint under all expected faults and normal states, the dispatching result is relatively simple to operate, and the economy is poor; or the overloading power flow and the out-of-limit voltage are adjusted to the safe range by taking generator group rescheduling, load shedding and other control measures after the accident, the economy is good, but this method allows the line power flow to exceed the limit after the fault, the safety is poor, and the operation is difficult. For the security constrained optimal power flow problem of the AC / DC power grid, the existing technology cannot guarantee that the AC / DC power grid is always safe, stable and economic. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the application provides a security constrained optimal power flow control method and system for an AC / DC hybrid power grid. The purpose of the method and system is to provide a preventive correction combined control security constrained optimal power flow method applied to an AC / DC power grid, which is essentially a nonlinear optimization problem with constraints, and finally an optimal solution is obtained by means of an intelligent algorithm, and in the case that the AC / DC power grid is in heavy load, weak operation mode and the like, the system is always operated at the optimal operating point by adjusting the generator output and load shedding.

[0005] The solution adopted to achieve the above-mentioned purpose is as follows:

[0006] A security constrained optimal power flow control method for an AC / DC hybrid power grid, which is improved in that it comprises:

[0007] The operating data of the generators, AC buses and DC nodes in the AC / DC hybrid power grid are input into a pre-established preventive correction control security constrained optimal power flow model to obtain optimal rescheduling amounts of the generator output and optimal rescheduling amounts of the load;

[0008] According to the output optimal rescheduling quantity and the load optimal rescheduling quantity, the generator output and the load consumption are adjusted.

[0009] The preventive-correction control security constrained optimal power flow model comprises security constrained optimal power flows of preventive control stages and correction control stages.

[0010] The preventive-correction control security constrained optimal power flow model comprises security constrained optimal power flows of preventive control stages and correction control stages.

[0011] The objective function is constructed by taking the minimization of operation risk as a target and considering the minimization of power generation cost.

[0012] The security constrained optimal power flow condition of preventive-correction control is constructed.

[0013] The security constrained optimal power flow condition of preventive-correction control comprises power balance constraints of DC and AC nodes in preventive and correction control stages, generator and load power constraints, node voltage constraints and branch power flow constraints.

[0014] The AC-DC hybrid power grid comprises:

[0015] The AC-DC hybrid power grid comprises:

[0016] The generator power constraint is shown in the following formula:

[0017]

[0018]

[0019] In the formula, P g,o corr Q g,o corr Q P Q P Q P The constraint conditions are as follows:

[0020]

[0021]

[0022] In the formula, Pmin g represents the minimum active power of the gth generator in the prevention and correction control stage, Pmax g represents the maximum active power of the gth generator in the prevention and correction control stage; Qmin g represents the minimum reactive power of the gth generator in the prevention and correction control stage, Qmax g represents the maximum reactive power of the gth generator in the prevention and correction control stage.

[0023] The fourth preferred technical solution provided by the application improves in that the load power constraint is as follows:

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031] In the formula, Pmin m represents the active power of the mth load in the prevention control stage, Qmin m represents the reactive power of the mth load in the prevention control stage; P0 m represents the initial reference value of the active power of the mth load, Q0 m represents the initial reference value of the reactive power of the mth load; Pcor m represents the active power of the mth load in the correction control stage, Qcor m represents the reactive power of the mth load in the correction control stage; Pcor m represents the active power of the mth load in the correction control stage, Qcor m represents the reactive power of the mth load in the correction control stage; And The constraint conditions are as follows:

[0032]

[0033]

[0034] representing the active power minimum of the mth load in the case of the occurrence of the contingency o, representing the reactive power minimum of the mth load in the case of the occurrence of the contingency o.

[0035] The fifth preferred technical solution provided by the application improves in that the operation data of the generators, the AC bus and the DC node in the AC-DC hybrid power grid are input into the pre-established preventive correction control security constrained optimal power flow model to obtain the optimal rescheduling amount of the generator output and the optimal rescheduling amount of the load, and the method comprises the following steps:

[0036] The operation data of the generators, the AC bus and the DC node in the AC-DC hybrid power grid are input into the pre-established preventive correction control security constrained optimal power flow model;

[0037] The preventive correction control security constrained optimal power flow model is solved by using the Matlab optimal power flow calculation program to obtain the optimal rescheduling amount of the generator output and the optimal rescheduling amount of the load;

[0038] The operation data of the generators comprises the active and reactive power of the generators; the operation data of the AC bus comprises the voltage and phase angle of the AC bus; and the operation data of the DC node comprises the voltage of the DC node.

[0039] The sixth preferred technical solution provided by the application improves in that the output of the generators and the consumption of the load are adjusted according to the optimal rescheduling amount of the output and the optimal rescheduling amount of the load, and the method comprises the following steps:

[0040] In the preventive control stage, the active and reactive power of the generators is adjusted according to the rescheduling amount of the active and reactive power of the generators in the preventive control stage;

[0041] In the correction control stage, the active and reactive power of the generators is adjusted according to the rescheduling amount of the active and reactive power of the generators in the correction control stage, and the active and reactive power of the load consumption is adjusted according to the rescheduling amount of the active and reactive power of the load in the correction control stage;

[0042] The optimal rescheduling amount of the output comprises the rescheduling amount of the active and reactive power of the generators in the preventive control stage and the rescheduling amount of the active and reactive power of the generators in the correction control stage; and the optimal rescheduling amount of the load comprises the rescheduling amount of the active and reactive power of the load in the correction control stage.

[0043] The seventh preferred technical solution provided by the application is improved in that the target function is shown in the following formula:

[0044]

[0045] In the formula, F represents the target function, the superscript prev represents the preventive control stage, the superscript corr represents the correction control stage, the subscript g represents the gth generator, and the subscript n represents the nth generator shedding load;

[0046] represents the total re-dispatching cost of the G generators in the preventive control stage; represents the re-dispatching cost coefficient of the gth generator in the preventive control stage; represents the set value P g prev of the gth generator in the preventive control stage, g ref the deviation of the set value P is calculated as follows:

[0047]

[0048] represents the re-dispatching operation risk in the correction control stage, O represents the set of expected faults, o represents an expected fault in the set of expected faults, and p o represents the probability of the occurrence of the expected fault o;

[0049] represents the total re-dispatching cost of the G generators in the correction control stage; C g corr represents the re-dispatching cost coefficient of the gth generator in the correction control stage; represents the set value P g corr of the gth generator in the correction control stage, g prev the deviation of the set value P is calculated as follows:

[0050]

[0051] represents the total load shedding cost of the N generators shedding load in the correction control stage; C n corr represents the load shedding cost coefficient of the nth generator in the correction control stage; represents the set value P n,o of the nth generator shedding load in the correction control stage.corr deviation between the initial reference value P n ref deviation between the initial reference value P is calculated as follows:

[0052]

[0053] The application discloses a security-constrained optimal power flow control system of an AC-DC hybrid power grid.

[0054] The optimization calculation module is used for inputting the operation data of the generators, the AC bus and the DC node in the AC-DC hybrid power grid into a pre-established security-constrained optimal power flow model of preventive correction control to obtain optimal rescheduling amounts of the generator output and the load.

[0055] The execution module is used for adjusting the generator output and the load consumption according to the optimal rescheduling amounts of the generator output and the load.

[0056] The security-constrained optimal power flow model of preventive correction control comprises security-constrained optimal power flows in the preventive control stage and the correction control stage.

[0057] The eighth preferred technical scheme of the application further comprises a modeling module used for establishing the security-constrained optimal power flow model of preventive correction control, and the modeling module comprises a target function unit and a constraint condition unit.

[0058] The target function unit is used for constructing a target function with the minimization of operation risk as a target while considering the minimization of power generation cost.

[0059] The constraint condition unit is used for constructing the security-constrained optimal power flow condition of preventive correction control.

[0060] The security-constrained optimal power flow condition of preventive correction control comprises power balance constraints of the DC and AC nodes in the preventive and correction control stages, generator and load power constraints, node voltage constraints and branch power flow constraints.

[0061] Compared with the closest prior art, the application has the following beneficial effects:

[0062] The application inputs operation data in an AC / DC hybrid power grid into a pre-established preventive correction control security constrained optimal power flow model to obtain optimal rescheduling of generator output and optimal rescheduling of load; and adjusts generator output and load consumption according to the optimal rescheduling of generator output and the optimal rescheduling of load; compared with the prior art, the significant feature is that the preventive control security constrained optimal power flow is combined with the correction control security constrained optimal power flow and applied to the AC / DC hybrid power grid to realize optimal decision of the AC / DC hybrid power grid giving consideration to economy and reliability.

[0063] In the application, for all possible expected accidents in the AC / DC hybrid power grid, the preventive control security constrained optimal power flow calculation is first adopted to effectively limit post-fault line flow and reduce post-fault overload level, and then the generator unit rescheduling or load shedding is solved by the correction control security constraint to solve the problem of overloading and voltage out-of-limit. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 A safety constraint optimal power flow control method flowchart of an AC / DC hybrid power grid provided by the application is shown in the figure.

[0065] Fig. 2(a) is an equivalent model schematic diagram of an AC line involved in the application;

[0066] Fig. 2(b) is an equivalent model schematic diagram of a DC line involved in the application;

[0067] Figure 3 Fig. 1 is an equivalent model schematic diagram of an AC / DC converter station involved in the application;

[0068] Figure 4 Fig. 5 is an IEEE 5-node test system schematic diagram involved in an embodiment of the application;

[0069] Figure 5 Fig. 6 is a basic structure schematic diagram of a safety constraint optimal power flow control system of an AC / DC hybrid power grid provided by the application;

[0070] Figure 6 Fig. 7 is a detailed structure schematic diagram of a safety constraint optimal power flow control system of an AC / DC hybrid power grid provided by the application. DETAILED DESCRIPTION

[0071] The specific embodiments of the application are further described in detail below with reference to the accompanying drawings.

[0072] Embodiment 1

[0073] A safety constraint optimal power flow control method flowchart of an AC / DC hybrid power grid provided by the application is shown in the figure. Figure 1

[0074] ​Step 1: input the operation data of the generator, AC bus and DC node in the AC-DC hybrid power grid into the pre-established preventive correction control security constrained optimal power flow model to obtain optimal rescheduling amount of generator output and optimal rescheduling amount of load;

[0075] Step 2: adjust the generator output and load consumption according to the optimal rescheduling amount of generator output and the optimal rescheduling amount of load;

[0076] The preventive correction control security constrained optimal power flow model includes security constrained optimal power flow in the preventive control stage and the correction control stage.

[0077] A security constrained optimal power flow control method for an AC-DC hybrid power grid includes the following steps:

[0078] Step 11: establish an objective function of the preventive correction control security constrained optimal power flow problem of the AC-DC hybrid power grid.

[0079] In step 11, the objective function F is constructed with the minimum operation risk and the minimum generation cost as the target, that is,

[0080]

[0081] In the formula, represents the total rescheduling cost of G generators in the preventive control, wherein and are the corresponding coefficients and the deviation of the set value of the gth generator in the preventive control stage from the initial reference value, respectively; represents the operation risk of the correction control rescheduling, wherein O is a set of expected faults, o is a given expected fault in the set of expected faults, p o represents the probability of occurrence of the expected fault, represents the total rescheduling cost of G generators in the correction control, represents the total cost of N generators shedding load in the correction control, C g corr , and C n corr are the corresponding coefficients, respectively, is the deviation of the set value of the gth generator output in the correction control stage from the set value in the preventive control stage when the given expected fault o occurs; is the deviation of the set value P n,o corr of the nth generator output in the correction control stage from the initial reference value P n ref .

[0082] Step 12: establish the constraint condition of the preventive correction control security constrained optimal power flow problem of the AC-DC hybrid power grid.

[0083] The AC-DC hybrid power grid comprises an AC branch, a DC branch, a converter transformer, a filter, a phase reactor and a converter.

[0084] The constraint conditions of the full-constraint optimal power flow problem comprise a node power balance constraint, a generator and load power constraint, a node voltage constraint and a branch power flow constraint.

[0085] Step 13: The established preventive and corrective control safety-constrained optimal power flow model is solved by using a Matlab optimal power flow calculation program, and then the optimal power flow of the AC-DC hybrid power grid is realized by adjusting the generator output and load shedding to the optimal values.

[0086] In step 13, the established AC-DC power grid preventive and corrective control safety-constrained optimal power flow model is a constrained nonlinear programming, which can be solved by using intelligent algorithms such as genetic algorithm and particle swarm optimization algorithm, and realized by computer language programming.

[0087] In step 13, the generator output adjustment comprises output adjustment in the preventive control phase and output adjustment in the corrective control phase, and the load shedding adjustment comprises load shedding adjustment in the corrective control phase. The load shedding is the load rescheduling.

[0088] Embodiment 2:

[0089] The specific implementation method of the present application will be described in detail below in combination with the drawings in the embodiments of the present application. In order to facilitate understanding, first, the commonly used letter marks appearing in the following description are briefly described.

[0090] Superscript:

[0091] prev represents the preventive control phase;

[0092] corr represents the corrective control phase;

[0093] mag represents the amplitude;

[0094] ac represents AC;

[0095] dc represents DC;

[0096] tf represents the converter transformer;

[0097] pr represents the phase reactor;

[0098] cv represents the converter;

[0099] f represents the filter;

[0100] out represents an output electrical quantity;

[0101] rated represents a rated value;

[0102] max represents a maximum value;

[0103] min represents a minimum value;

[0104] ref represents an initial reference value;

[0105] loss represents a loss;

[0106] subscript:

[0107] o represents a contingency o;

[0108] lij, lji represent one end node i to the other end node j of an alternating current line l and its reverse direction, respectively;

[0109] def, dfe represent one end node e to the other end node f of a direct current line d and its reverse direction, respectively;

[0110] cie, cei represent one end alternating current node i to the other end direct current node e and one end direct current node e to the other end alternating current node i, respectively.

[0111] Specifically, a security-constrained optimal power flow control method for an AC / DC hybrid power grid comprises:

[0112] Step 101: Establishing an objective function of a security-constrained optimal power flow problem of the AC / DC hybrid power grid for preventive and corrective control. That is, establishing an objective function of a preventive and corrective control security-constrained optimal power flow model.

[0113] With the objective of minimizing the operational risk, a target function F is constructed by considering the minimum generation cost, that is:

[0114]

[0115] In formula (1), subscript g represents the gth generator, and subscript n represents the nth generator of load shedding. represents the total rescheduling cost of the G generators in the preventive control, is the rescheduling cost coefficient of the gth generator in the preventive control stage, is calculated according to the following formula, and its value depends on the set value P g prev of the gth generator output in the preventive control stage. g ref The deviation of the initial reference value P

[0116]

[0117] represents the risk of the re-dispatching of the G generators in the corrective control phase, C o represents the probability of the occurrence of the contingency o.

[0118] represents the total cost of the re-dispatching of the N generators in the corrective control phase, which cost function is multiplied by the probability p of the occurrence of the contingency o o , obtaining the risk index of the re-dispatching of the N generators in the corrective control phase in the presence of the contingency o, C g corr is the re-dispatching cost coefficient of the gth generator in the corrective control phase, is calculated according to the following formula, whose value depends on the deviation, with polynomial nature, of the set value P g corr from the set value P g prev in the preventive control phase.

[0119]

[0120] represents the total cost of the re-dispatching of the N generators in the corrective control phase, which cost function is multiplied by the probability p of the occurrence of the contingency o o , obtaining the risk index of the re-dispatching of the N generators in the corrective control phase in the presence of the contingency o, C n corr is the re-dispatching cost coefficient of the nth generator in the corrective control phase, is calculated according to the following formula, whose value depends on the deviation, with polynomial nature, of the set value P n,o corr from the initial reference value P n ref .

[0121]

[0122] Step 102: establishing a mathematical description of the AC-DC hybrid power grid.

[0123] The AC-DC hybrid power grid comprises AC branches, DC branches, converter transformers, filters, phase reactors and converters; based on the topology of the AC-DC hybrid power grid, the structures constituting the AC-DC hybrid power grid are mathematically described.

[0124] First, equivalent mathematical descriptions of AC and DC lines in a hybrid AC / DC power grid are established. The AC lines are mathematically described using the π equivalent model, and the resulting equivalent mathematical description of the AC lines is shown in Figure 2(a).

[0125] During the prevention and control phase, the active power P on the AC branch l from any node i to node j in the AC network... lij ac,prev and reactive power Q lij ac,prev Defined as:

[0126]

[0127] In equation (5), g and b are the series conductance and susceptance of the line, respectively; g fr b fr These are the parallel conductance and susceptance at node i, respectively; U i mag,prev U j mag,prev These represent the voltage amplitudes at node i and node j respectively during the prevention and control phase. These represent the voltage phase angles of nodes i and j during the prevention and control phase, respectively.

[0128] During the prevention and control phase, the active power P from node j to node i in the opposite direction is... lji ac,prev and reactive power Q lji ac,prev It is then defined as:

[0129]

[0130] In equation (6), g to b to These are the parallel conductance and susceptance at node j, respectively.

[0131] During the correction control phase, in the event of a anticipated fault o, the active power P flowing from node i to node j in the non-faulty AC branch l... lij,o ac,corr and reactive power Q lij,o ac,corr The following formula is used to calculate:

[0132]

[0133] In equation (7), U i mag,corr U j mag,corr θ represents the voltage amplitudes at nodes i and j respectively during the correction control phase. i corr θ j corrVei and Vej represent the voltage phase angle of node i and node j respectively in the corrective control phase.

[0134] When branch I is faulted, the active power P lij,o ac,corr,out and the reactive power Q lij,o ac,corr,out are defined as zero:

[0135]

[0136] In the preventive and corrective control phase, the active and reactive power flow in AC branch I, whether it is from node i to j or from node j to i, should be within the range of the apparent power rating S l rated,ac i.e.:

[0137]

[0138] The equivalent mathematical description of DC line is shown in Fig. 2(b). For the monopole HVDC system, all the power flow is in one pole, while for the symmetric monopole and bipolar HVDC system, the power flow is in the positive pole and the negative pole respectively. Therefore, the power flow of DC line should be treated accordingly according to the different number of poles p d (p d ∈{1, 2}).

[0139] According to Fig. 2(b), the power flow of DC branch can be expressed as:

[0140]

[0141] In equation (10), and P dfe dc represent the active power from DC node e to node f and from DC node f to node e respectively, P d dc,loss represents the loss of DC branch d, and In the preventive and corrective control phase, the power flow should be within the range of the rating of DC branch P d dc,rated

[0142]

[0143] In the preventive control phase, the active power flow from DC node e to node f P is calculated according to the following equation:

[0144]

[0145] In equation (12), U e ​dc,prev , are the voltages at DC nodes e and f respectively in the preventive control phase, g d s is the series conductance of DC branch d.

[0146] For the correction control phase, in case of the contingency o, the DC power P def,o dc,corr is calculated according to:

[0147]

[0148] In equation (13), U e,o dc,corr , U f,o dc,corr are the voltages at DC nodes e and f respectively in the correction control phase.

[0149] When a fault occurs in branch d, the power flow P def,o dc,corr,out between DC nodes e and f is defined as zero, i.e.

[0150]

[0151] The equivalent mathematical description of an AC / DC converter station is established according to Figure 3 including transformers with taps and series impedances, filters, phase reactors, power electronic AC / DC converters. Transformers, filters and phase reactors are passive elements and are described by classical power models. The converter type can be LCC, VSC or MMC and operates in inverter or rectifier state. In the figure, represents the AC voltage at node i, where U i mag , θ i are the amplitude and phase angle of U i , respectively; U e dc represents the DC voltage at node e; represents the filter voltage, is the amplitude and phase angle of U , respectively; represents the converter outlet voltage.

[0152] The converter transformer impedance is assumed to be z c tf = r c tf + jx c tf , and in admittance form y c tf = g c tf+jb c tf 。t c is the tap of the converter transformer. In the preventive control stage, the active power P cie tf,prev and the reactive power Q cie tf,prev are calculated by taking the flow from the AC node i to the DC node e as the positive direction.

[0153]

[0154] In the formula (15), U i mag,prev , respectively represent the AC voltage amplitude of the node i in the preventive control stage and the voltage amplitude of the filter, and θ i prev , θ c f,prev respectively represent the phase angle of the AC voltage of the node i in the preventive control stage and the phase angle of the voltage of the filter.

[0155] The active power P cei tf,prev and the reactive power Q cei tf ,prev are calculated by taking the flow from the DC node e to the AC node i as the positive direction.

[0156]

[0157] In the corrective control stage, the active power P

[0158]

[0159] In the formula (17), P cie,o tf,corr , Q cie,o tf,corr respectively represent the active power and the reactive power through the converter transformer in the corrective control stage by taking the flow from the AC node i to the DC node e as the positive direction; P cei,o tf,corr , Q cei,o tf,corr represent the active power and the reactive power through the converter transformer in the corrective control stage by taking the flow from the DC node e to the AC node i as the positive direction; U i mag,corr , respectively represent the AC voltage amplitude of the node i in the corrective control stage and the voltage amplitude of the filter, and θ i corr , θ c,of,corr These represent the AC voltage at node i in the correction control phase and the voltage phase angle of the filter, respectively.

[0160] For the converter transformer in the faulty branch, the output active power P cie,o tf,corr,out P cei,o tf,corr,out and reactive power Q cie,o tf,corr,out Q cei,o tf,corr,out The unified definition is zero, that is

[0161]

[0162] If there is no converter transformer on the line, or numerically... The following formula applies to components that do not experience losses during the prevention and correction control phase:

[0163]

[0164] In equation (19), P cie tf and Q cie tf P represents the active power and reactive power flowing through the converter transformer when the flow direction from node i to e is considered positive; cei tf and Q cei tf These represent the active power and reactive power flowing through the converter transformer when the flow direction from node e to i is the positive direction, respectively. and θ i These represent the voltage magnitude and phase angle at node i, respectively. and These represent the voltage amplitude and phase angle of the filter, respectively.

[0165] Filters are currently mainly used in LCC-HVDC systems to filter out harmonics on the line. Assume the susceptance of the parallel capacitor is b. c f Reactive power Q during the prevention and control phase c f,prev In the event of a anticipated fault during the correction control phase, the reactive power Q of the filter in the non-faulty branch is... c,o f,corr The calculation is as follows:

[0166]

[0167] For the reactive power Q of the filter in all branches where the anticipated fault occurs c,o f,corr,out have

[0168]

[0169] For phase reactors, assume the impedance of the phase reactor is z c pr = r c pr + jx c pr The admittance form is y c pr = g c pr + jb c pr The power flow calculation formula is consistent with the converter transformer, that is, set the transformer tap t c in equations (15) - (17) to 1.

[0170] In the preventive and corrective control phase, the power flow between the filter capacitor, phase reactor and converter transformer is generally balanced, that is:

[0171]

[0172] In equation (22), P cie pr and Q cie pr are the active power and reactive power through the phase reactor in the positive direction from node i to node e; P cei pr and Q cei pr are the active power and reactive power through the phase reactor in the positive direction from node e to node i; Q c f represents the filter reactive power.

[0173] For AC / DC converters, assume P c cv,ac and Q c cv,ac are the active and reactive power exchanges at the AC outlet bus of the converter. In the preventive and corrective control phase, the active and reactive power must follow the following constraints:

[0174]

[0175] In equation (23), the superscripts prev, corr, min and max have the same meaning as described above; S c cv,ac,rated represents the apparent power rating at the AC outlet bus of the converter.

[0176] In the preventive and corrective control phase, the active power P ccv,dc The following constraints must be obeyed:

[0177]

[0178] In formula (24), the superscripts prev, corr, min and max have the same meaning as in formula (23).

[0179] For the converter in which the anticipated faulty branch occurs in the correction phase, the DC-side power P c.o cv,dc,corr,out is zero, i.e.:

[0180]

[0181] The AC-side active power P c cv,ac and the DC-side active power P c cv,dc satisfy the following equation

[0182]

[0183] In formula (26), P c cv,loss represents the self-loss of the converter, which is generally calculated by the following formula:

[0184]

[0185] wherein a c cv represents the no-load loss of the transformer and the average loss of auxiliary equipment, b c cv represents the average loss of the valve and the freewheeling diode, and c c cv represents the conduction loss of the valve, and a c cv ≥ 0 (W), b c cv ≥ 0 (W / A), and c c cv ≥ 0 (Ω); represents the AC-side current amplitude of the converter.

[0186] The AC-side active power P c cv,ac and the AC-side reactive power Q c cv,ac satisfy the following constraints,

[0187]

[0188] In formula (28), I c cv,mag , Ic cv,rated U c cv U c cv ,min U c cv,max U c cv,mag,prev U c cv,mag,prev U c,o cv,mag,corr U c,o cv,mag,corr

[0189] P c,o cv,ac,corr,out Q c,o cv,ac,corr,out I c,o cv,mag,corr

[0190]

[0191] I c cv,dc

[0192]

[0193] I c cv,dc,mag I c cv,dc,min I c cv,dc,max

[0194] c cv,ac c cv,ac

[0195]

[0196] is the thyristor firing angle, and has​​​​​​​​

[0197] Step 103: Establish the constraint conditions of the preventive and corrective control security constrained optimal power flow model of the AC / DC hybrid power grid.

[0198] The constraint conditions include:

[0199] (1) Power balance equation of each node

[0200] In the preventive and corrective control phase, for the DC node e of the AC / DC network, there are:

[0201]

[0202] In formula (32), E represents the number of all converter branches connected to the DC node e, F represents the number of all DC branches connected to the DC node e, M,dc represents the number of all DC loads connected to the DC node e, P m dc represents the active power of the mth DC load connected to the DC node e; P c cv,dc,prev represents the active power of the DC side of the converter in the preventive control phase; represents the active power from the one end node e to the other end node f of the DC line in the preventive control phase; represents the active power of the DC side of the converter in the corrective control phase under the condition that the contingency o occurs; represents the active power from the one end node e to the other end node f of the DC line in the corrective control phase under the condition that the contingency o occurs.

[0203] For the AC side of the AC / DC network, the node balance equation in the preventive control phase is:

[0204]

[0205] In formula (33), P g prev , Q g prev represent the active and reactive power output by the generator, respectively, P m prev , Q m prev represent the active and reactive power consumed by the AC load, respectively, g i shunt , b i shunt are the shunt conductance and susceptance of the AC bus, I represents the number of all converter branches connected to the AC node i, J represents the number of all AC branches connected to the AC node i, G represents the number of generators connected to the AC node i, and M,ac represents the number of all AC loads connected to the AC node i. This indicates the active power flowing from AC node i to DC node e during the prevention and control phase, through the converter transformer. This indicates the reactive power flowing from AC node i to DC node e during the prevention and control phase, through the converter transformer. This represents the active power flowing from AC node i to AC node j on AC line l during the prevention and control phase. This represents the reactive power flowing from AC node i to AC node j on AC line l during the prevention and control phase.

[0206] The nodal equilibrium equations for the correction control phase are as follows:

[0207]

[0208] In equation (34), P g,o corr Q g,o corr P represents the active and reactive power output of the generator under the condition of the anticipated fault o. m corr Q m corr These represent the active and reactive power consumed by the load in the event of the anticipated fault o; This indicates that, under the condition of anticipated fault o, the corrective control phase takes the flow from AC node i to DC node e as the positive direction, and the active power through the converter transformer... This indicates that in the event of a anticipated fault o, the corrective control phase takes the flow from AC node i to DC node e as the positive direction, and the reactive power through the converter transformer; This represents the active power flowing from AC node i to AC node j on AC line l during the correction control phase in the event of a anticipated fault o. This represents the reactive power flowing from AC node i to AC node j on AC line l during the correction control phase in the event of a anticipated fault o. This represents the voltage amplitude of AC node i during the correction control phase.

[0209] (2) Other constraints

[0210] Generator active power P during prevention and correction control phase g reactive power P g The output must comply with the following constraints:

[0211]

[0212] In the formula, This represents the minimum active power of the g-th generator during the prevention and correction control phase. P g (P g ) max (prevention and correction control phase) Q g (P g ) min (prevention and correction control phase) Q g (P g ) max (prevention and correction control phase)

[0213] P g (P g ) max (prevention control phase) Q g (P g ) min (prevention control phase)

[0214]

[0215] P g (P g ) max (prevention control phase) g prev Q g (P g ) min (prevention control phase) g prev The active and reactive power outputs should be set according to the following equations:

[0216]

[0217] where and represent the initial reference values of the active and reactive power of the gth generator, respectively.

[0218] In the correction control phase, for each possible contingency o in the set of contingencies O, the active and reactive power output rescheduling quantities The following constraints should be followed:

[0219]

[0220] Therefore, in the correction control phase, the active P g,o corr and reactive Q g,o corr power outputs of the generators should be set according to the following equations:

[0221]

[0222] The prevention control phase does not allow load shedding, therefore the active P m prev and reactive Q m prev loads of this phase remain unchanged, i.e.

[0223]

[0224] where represents the initial reference value of the active power of the mth load, represents the initial reference value of the reactive power of the mth load.

[0225] In the correction control phase, the active Pm,o corr , reactive Q m,o corr and rescheduling quantity The constraint condition is

[0226]

[0227]

[0228] wherein, represents the active power minimum value of the mth load in the case that the expected fault o occurs, represents the reactive power minimum value of the mth load in the case that the expected fault o occurs.

[0229] The load in the correction control stage should be set according to the following formula:

[0230]

[0231] and the active and reactive power values P m,o corr , Q m,o corr have the following relationship:

[0232]

[0233] In the preventive control and correction control stages, the node voltage should satisfy:

[0234]

[0235] In the formula, represents the voltage amplitude of the alternating node i, represents the minimum value of , represents the maximum value of represents the voltage of the direct current side node e, represents the maximum value of represents the minimum value of

[0236] In the preventive control and correction control stages, the alternating and direct current branch flow constraints are respectively shown in the above formula (9) and formula (11)

[0237] Step 104: solving the preventive correction control security constraint optimal power flow model.

[0238] ​​​​The established optimal power flow model with safety constraints for preventive and corrective control was implemented using Matlab programming. Parameters such as generator active and reactive power, AC bus and DC node voltages and phase angles, and initial setpoints for load active and reactive power were input. A genetic algorithm was then used to solve the problem, yielding the optimal solution for the state variables in the AC / DC hybrid power grid, i.e., the generator output rescheduling amount during the preventive control phase. Generator output rescheduling during correction control phase and load rescheduling

[0239] Finally, the state variables in the AC / DC hybrid power grid (generator output rescheduling during the preventive control phase) are discussed. Generator output rescheduling during correction control phase and load rescheduling The optimal solution is assigned so that the power grid operates at the optimal operating point, thereby minimizing the generation cost and system operation risk.

[0240] Step 105: Execute the obtained optimal solution.

[0241] Assigning optimal solutions to the state variables in an AC / DC hybrid power grid, i.e., during the preventive control phase, based on... Adjust the generator output during the calibration control phase according to... Adjust the generator output according to Adjusting the active and reactive power consumed by the load to ensure the power grid operates at its optimal operating point, thereby minimizing power generation costs and system operation risks.

[0242] Example 3:

[0243] The following is a specific example.

[0244] Based on the mathematical model proposed in this invention, software for calculating the optimal power flow under the safety constraints of preventive correction control in AC / DC hybrid power grids was developed using the MATLAB programming language, and simulation verification was performed on the IEEE 5-bus test system. Figure 4 As shown, a 3-node DC grid is interconnected with a 5-node AC system via a VSC. The simulation assumes a failure probability of 1, thus analyzing a typical case of the N-1 safety criterion. The load shedding cost is set at $5000 / MWh.

[0245] Table 1 presents the optimal power flow results under security constraints for the simulation examples, yielding the minimum objective function values ​​for various cases. Example 1 considers the case where there is no DC grid and only the anticipated fault occurs in the AC grid; Example 2 considers the case where only the AC system experiences the anticipated fault in the AC / DC hybrid grid; and Example 3 considers the case where only the DC system experiences the anticipated fault in the AC / DC hybrid grid.

[0246] Table 1: Security constrained optimal power flow results

[0247]

[0248] Example 4:

[0249] Based on the same inventive concept, the application also provides a security constrained optimal power flow control system of an AC / DC hybrid power grid. Since the principles of these devices for solving the technical problems are similar to the security constrained optimal power flow control method of the AC / DC hybrid power grid, the repeated parts will not be described again.

[0250] The basic structure of the system is shown in Figure 5 , and includes an optimization calculation module and an execution module.

[0251] The optimization calculation module is configured to input the operation data of the generators, AC buses and DC nodes in the AC / DC hybrid power grid into a pre-established preventive correction control security constrained optimal power flow model to obtain optimal rescheduling amounts of generator outputs and optimal rescheduling amounts of loads.

[0252] The execution module is configured to adjust the generator outputs and load consumptions according to the optimal rescheduling amounts of generator outputs and the optimal rescheduling amounts of loads.

[0253] The preventive correction control security constrained optimal power flow model includes security constrained optimal power flows in the preventive control stage and the correction control stage.

[0254] The detailed structure of the security constrained optimal power flow control system of the AC / DC hybrid power grid is shown in Figure 6 .

[0255] The system further includes a modeling module for establishing the preventive correction control security constrained optimal power flow model, and the modeling module includes a target function unit and a constraint condition unit.

[0256] The target function unit is configured to construct a target function with the minimization of operation risk as the target while considering the minimization of power generation cost.

[0257] The constraint condition unit is configured to construct security constrained optimal power flow conditions for preventive correction control.

[0258] The security constrained optimal power flow conditions for preventive correction control include power balance constraints of DC and AC nodes in the preventive and correction control stages, generator and load power constraints, node voltage constraints, and branch power flow constraints.

[0259] The optimization calculation module includes a data input unit and a solution unit.

[0260] The data input unit is configured to input operation data of a generator, an AC bus and a DC node in the AC-DC hybrid power grid into a pre-established preventive correction control security constrained optimal power flow model.

[0261] The solving unit is configured to solve the preventive correction control security constrained optimal power flow model by using a Matlab optimal power flow calculation program to obtain optimal rescheduling amounts of generator output and optimal rescheduling amounts of load.

[0262] The operation data of the generator includes active and reactive power of the generator, the operation data of the AC bus includes voltage and phase angle of the AC bus, and the operation data of the DC node includes voltage of the DC node.

[0263] The execution module includes a preventive control stage execution unit and a correction control stage execution unit.

[0264] The preventive control stage execution unit is configured to adjust active and reactive power of the generator according to the active and reactive power rescheduling amounts of the generator in the preventive control stage.

[0265] The correction control stage execution unit is configured to adjust active and reactive power of the generator according to the active and reactive power rescheduling amounts of the generator in the correction control stage, and adjust active and reactive power consumed by the load according to the active and reactive power rescheduling amounts of the load in the correction control stage.

[0266] The optimal rescheduling amounts include the active and reactive power rescheduling amounts of the generator in the preventive control stage and the active and reactive power rescheduling amounts of the generator in the correction control stage, and the optimal rescheduling amounts of the load include the active and reactive power rescheduling amounts of the load in the correction control stage.

[0267] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system or a computer program product. Therefore, the present application can be in the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware aspects. Moreover, the present application can be in the form of a computer program product implemented on one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program code.

[0268] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flow or blocks. Figure 1 one or more flow or blocks.

[0269] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart block or blocks. Figure 1 one or more flow or blocks. Figure 1 one or more flow or blocks.

[0270] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flow or blocks. Figure 1 one or more flow or blocks.

[0271] Finally, it should be noted that the above-described embodiments are merely used to illustrate the technical solutions of the present application, but are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical personnel in the field can make various changes, modifications or equivalent replacements to the specific embodiments of the present application after reading the present application. However, these changes, modifications or equivalent replacements are within the scope of protection of the claims of the present application.

Claims

1. A method for security constrained optimal power flow control of an AC / DC hybrid power grid, characterized in that, The method comprises the steps of: inputting operation data of generators, AC buses and DC nodes in an AC-DC hybrid power grid into a pre-established preventive-correction control security constrained optimal power flow model to obtain optimal rescheduling amounts of generator outputs and optimal rescheduling amounts of loads; adjusting the generator outputs and load consumptions according to the optimal rescheduling amounts of the generator outputs and the optimal rescheduling amounts of the loads; wherein the preventive-correction control security constrained optimal power flow model comprises security constrained optimal power flows in a preventive control stage and a correction control stage; the establishment of the preventive-correction control security constrained optimal power flow model comprises: constructing an objective function with minimization of operation risk as a target while considering minimization of generation cost; constructing security constrained optimal power flow conditions for preventive-correction control; wherein the security constrained optimal power flow conditions for preventive-correction control comprise power balance constraints of DC and AC nodes in the preventive and correction control stages, generator and load power constraints, node voltage constraints and branch power flow constraints; the generator power constraint is shown in the following formula: where P g,o corr Pog,cor,cor (o) represents the active power of the gth generator in the corrective control phase in case of the occurrence of the contingency o, g,o corr Qog,cor,cor (o) represents the reactive power of the gth generator in the corrective control phase in case of the occurrence of the contingency o; Pog,pre (o) represents the active power of the gth generator after the completion of the preventive control phase, Qog,pre (o) represents the reactive power of the gth generator after the completion of the preventive control phase; Pog,cor,cor (o) represents the active power of the gth generator in the corrective control phase in case of the occurrence of the contingency o, Qog,cor,cor (o) represents the reactive power of the gth generator in the corrective control phase in case of the occurrence of the contingency o; and The constraint conditions are respectively shown in the following equations: wherein Pmin g represents the minimum active power of the gth generator in the preventive and corrective control phase, Pmax g represents the maximum active power of the gth generator in the preventive and corrective control phase; Qmin g represents the minimum reactive power of the gth generator in the preventive and corrective control phase, Qmax g represents the maximum reactive power of the gth generator in the preventive and corrective control phase.

2. The method of claim 1, wherein, the AC-DC hybrid power grid comprises: AC branches, DC branches, converter transformers, filters, phase reactors and converters.

3. The method of claim 1, wherein, the load power constraint is shown in the following formula: In the formula, This represents the active power of the m-th load during the prevention and control phase. This represents the reactive power of the m-th load during the prevention and control phase. This represents the initial reference value of the active power of the m-th load. This represents the initial reference value for the reactive power of the m-th load; This represents the active power of the m-th load during the correction control phase, assuming the anticipated fault o occurs. This represents the reactive power of the m-th load during the correction control phase in the event of a anticipated fault o. This represents the active power rescheduled amount for the m-th load during the correction control phase, assuming the anticipated fault o occurs. This represents the reactive power rescheduling amount of the m-th load during the correction control phase in the event of a anticipated fault o. and The constraints are shown in the following equations: Pmin,m (o) denotes the active power minimum of the mth load in case of the envisaged fault o, Qmin,m (o) denotes the reactive power minimum of the mth load in case of the envisaged fault o.

4. The method of claim 1, wherein, the inputting of the operation data of the generators, the AC buses and the DC nodes in the AC-DC hybrid power grid into the pre-established preventive-correction control security constrained optimal power flow model to obtain the optimal rescheduling amounts of the generator outputs and the optimal rescheduling amounts of the loads comprises: inputting the operation data of the generators, the AC buses and the DC nodes in the AC-DC hybrid power grid into the pre-established preventive-correction control security constrained optimal power flow model; solving the preventive-correction control security constrained optimal power flow model by using an optimal power flow calculation program of Matlab to obtain the optimal rescheduling amounts of the generator outputs and the optimal rescheduling amounts of the loads; wherein the operation data of the generators comprise active and reactive powers of the generators, the operation data of the AC buses comprise voltages and phase angles of the AC buses, and the operation data of the DC nodes comprise voltages of the DC nodes.

5. The method of claim 1, wherein, the adjusting of the generator outputs and the load consumptions according to the optimal rescheduling amounts of the generator outputs and the optimal rescheduling amounts of the loads comprises: in the preventive control stage, adjusting active and reactive powers of the generators according to the rescheduling amounts of the active and reactive powers of the generators in the preventive control stage; in the correction control stage, adjusting the active and reactive powers of the generators according to the rescheduling amounts of the active and reactive powers of the generators in the correction control stage and adjusting active and reactive powers of load consumptions according to the rescheduling amounts of the active and reactive powers of the loads in the correction control stage; wherein the optimal rescheduling amounts of the generator outputs comprise the rescheduling amounts of the active and reactive powers of the generators in the preventive control stage and the rescheduling amounts of the active and reactive powers of the generators in the correction control stage, and the optimal rescheduling amounts of the loads comprise the rescheduling amounts of the active and reactive powers of the loads in the correction control stage.

6. The method of claim 1, wherein, the objective function is shown in the following formula: In the formula, F represents a target function, the superscript prev represents a preventive control stage, the superscript corr represents a correction control stage, the subscript g represents the gth generator, and the subscript n represents the nth generator shedding load; represents the total sum of the rescheduling costs of the G generators in the preventive control phase; represents the rescheduling cost coefficient of the gth generator in the preventive control phase; represents the set value P of the gth generator in the preventive control phase g prev the deviation of the gth generator output P from the initial reference value P g ref is calculated as follows:​ represents the operational risk of rescheduling in the corrective control phase, O is the set of envisioned failures, o is an envisioned failure in the set of envisioned failures, p o represents the probability of the occurrence of the envisioned failure o; This represents the total cost of rescheduling G generators during the correction control phase; C g corr This represents the rescheduling cost coefficient during the correction control phase of the g-th generator; This indicates the setpoint P of the output of the g-th generator during the correction control phase, assuming the anticipated fault o occurs. g corr Compared with the prevention and control stage set value P g prev The deviation between them Calculate as follows: represents the total cost of the generator tripping in the correction control phase for N tripped generators; C n corr represents the tripping cost coefficient of the nth generator in the correction control phase; represents the set value of the nth tripped generator output in the correction control phase in the event of a predicted fault o n,o corr deviation between the initial reference value P n ref is calculated as follows:​ 7. A security constrained optimal power flow control system for an AC / DC hybrid power grid, characterized in that The method comprises the following steps: The optimization calculation module is configured to input the operation data of the generators, the AC bus and the DC nodes in the AC-DC hybrid power grid into a pre-established preventive-correction control safety constraint optimal power flow model to obtain optimal rescheduling amounts of generator output and load; The execution module is configured to adjust the generator output and load consumption according to the optimal rescheduling amounts of generator output and load. The preventive-correction control safety constraint optimal power flow model comprises safety constraint optimal power flows in the preventive control stage and the correction control stage. The method further comprises a modeling module configured to establish the preventive-correction control safety constraint optimal power flow model, and the modeling module comprises a target function unit and a constraint condition unit. The target function unit is configured to construct a target function with the minimum operation risk as the target while considering the minimum generation cost. The constraint condition unit is configured to construct safety constraint optimal power flow conditions for the preventive-correction control. The safety constraint optimal power flow conditions for the preventive-correction control comprise power balance constraints of the DC and AC nodes in the preventive and correction control stages, generator and load power constraints, node voltage constraints and branch power flow constraints. ​

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