Coordinated secondary voltage control method for ac-dc system considering dc control mode

Abstract

The application discloses a coordinated secondary voltage control method of an AC-DC system considering a DC control mode, which comprises the following steps: 1) establishing an external characteristic equation of a rectifier station and an inverter station connected to an AC system, and determining partial derivatives of active power transmission and reactive power consumption of the two converter stations to the amplitude of the converter bus voltage; 2) based on the external characteristic equation of the rectifier station and the inverter station connected to the AC system, a coordinated AC-DC secondary voltage control model M considering the correlation between a DC sending end and a receiving end is established; and 3) the coordinated AC-DC secondary voltage control model M considering the correlation between the DC sending end and the receiving end is solved by quadratic programming to obtain a coordinated secondary voltage control mode of the AC-DC system. The application can coordinate the reactive power output of a DC near-zone generator in a receiving end power grid, simultaneously consider the dynamic reactive power reserve level of the DC near zone, strengthen the control strength of the voltage level of the receiving end power grid, and improve the stability of the safe operation of the power grid.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system dispatch automation, in particular to a coordinated secondary voltage control method for AC / DC systems considering DC control mode. BACKGROUND

[0002] The construction of ultra-high voltage direct current (UHVDC) transmission projects is an objective requirement for the safe, efficient and clean supply of energy in China, and is an important part of the energy transformation strategy. At present, the layout of UHVDC and alternating current (AC) projects is not balanced, and both the sending end and the receiving end of the power grid show certain characteristics of "strong direct current and weak alternating current". At present, some UHVDCs are operated according to the peak and valley power transmission curves, and the DC power regulation needs to change the tap position of the converter transformer. The daily regulation will affect the service life of the tap device. On the other hand, the AC filter and compensation in the converter station also need to be switched in and out according to the change of DC power, and the average number of switch actions is much higher than that of the compensation equipment in general substations, which has a negative impact on the operation and service life of the switches in the converter station.

[0003] Therefore, it is necessary to fully utilize the advantages of flexible and controllable DC, make full use of the potential of the reactive power resources in the DC near area and the operation mode of the DC itself, improve the voltage and reactive power support capability of the DC near area in the receiving end, and reduce the number of actions of the transformer tap and filter switch in the converter station. The related theories and technologies need to be further studied. SUMMARY

[0004] The purpose of the present application is to provide a coordinated secondary voltage control method for AC / DC systems considering DC control mode, which comprises the following steps:

[0005] 1) establishing the external characteristic equation of the rectifier station and the inverter station connected to the AC system, and determining the partial derivative of the transmission active power and the consumption reactive power of the converter bus voltage amplitude of the two sides of the converter station;

[0006] The step of establishing the external characteristic equation of the rectifier station and the inverter station connected to the AC system, and determining the partial derivative of the transmission active power and the consumption reactive power of the converter bus voltage amplitude of the two sides of the converter station comprises:

[0007] 1.1) establishing the characteristic equation of the sending and receiving end converter, i.e.:

[0008]

[0009] In the formula, α is the trigger angle, γ is the off angle; N d , N r are the number of six-pulse converters per pole of the sending and receiving ends respectively; k pd , k pr are the number of operating poles of the sending and receiving converters respectively; T d = U dd0B / U ddB , Tr = U dr0B / U drB are the sending and receiving end reference value conversion factors respectively; U dd0B , U ddB are the sending end converter transformer valve side reference voltage and DC reference voltage respectively; U dr0B , U drB are the receiving end converter transformer valve side reference voltage and DC reference voltage respectively; Q dd , Q dr are the sending and receiving end converter consumed reactive power respectively; P dd , P dr are the sending and receiving end converter consumed active power respectively; I d is the current at the DC side of the converter station; U td , U tr are the sending and receiving end converter bus node voltage respectively; k Td , k Tr are the sending and receiving end converter station converter transformer transformation ratio respectively; X d , X r are the sending and receiving end converter station converter transformer equivalent reactance respectively; R d is the DC transmission line equivalent resistance. U dd0 , U dd are the sending end converter transformer valve side voltage and DC voltage respectively; U dr0 , U dr are the receiving end converter transformer valve side voltage and DC voltage respectively;

[0010] 1.2) When the DC system does not inject power to the AC system, the steady-state power flow equation of the pure AC system is established, i.e.:

[0011]

[0012] In the formula, △P and △Q are the imbalance matrices of the AC bus active power and reactive power respectively; △δ and △U are the correction matrices of the AC bus voltage phase angle and amplitude respectively; J Pδ , J PU , J Qδ , J QU are the four corresponding sub-matrices of the Jacobian matrix J.

[0013] 1.3) When the DC system injects power to the AC system, the diagonal elements of the sub-matrices J PU , J QU of the Jacobian matrix J are corrected, and the corrected elements J PU ’ and J QU ’ are as follows:

[0014]

[0015] where s i = 1 when node i is the sending converter bus node; s i = -1 when node i is the receiving converter bus node; U i is the voltage of node i; P dci , Q dci are the active power and reactive power of DC node i;

[0016] 1.4) The control equations of the sending and receiving converter station controllers are established, i.e.:

[0017]

[0018] where P dd is the DC power; γ is the turn-off angle of the inverter station; P dd sp , γ sp are the planned values of the DC transmission power and the turn-off angle of the inverter station.

[0019] 1.5) The external characteristic equations of the rectifier station and the inverter station connected to the AC system are established, i.e.:

[0020]

[0021] The partial derivatives of the active power transmitted by the two converter stations and the reactive power consumed by the two converter stations with respect to the amplitude of the converter bus voltage are as follows:

[0022]

[0023] where D d , D r are the related parameters for calculating the state variables of the sending and receiving DCs; is the partial derivative of the reactive power consumed by the sending converter station with respect to the voltage of the receiving converter bus;

[0024] where the partial derivative of the DC current with respect to the amplitude of the voltage of the receiving converter bus is as follows:

[0025]

[0026] 2) Based on the external characteristic equations of the rectifier station and the inverter station connected to the AC system, a coordinated AC / DC two-level voltage control model M considering the correlation between the sending and receiving DCs is established;

[0027] The objective function of the coordinated AC / DC two-level voltage control model M considering the correlation between the sending and receiving DCs is as follows:

[0028]

[0029] ​

[0030] where W c , W t and W q are weights, and W c > W q , W t > W q ; and are the initial value and the ideal reference value of the central node voltage vector, respectively, both of which have a dimension of n c × 1; and are the initial value and the set reference value of the receiving-end converter bus node voltage vector, respectively, both of which have a dimension of n dr × 1; n c , n g and n dr are the number of the AC central nodes, the controlled power plant nodes and the converter station nodes of the receiving-end power grid, respectively; C c , C t are the sensitivity matrices of the central node and the converter bus node voltage to the generator terminal voltage, respectively, both of which have a dimension of n c × n g , n dr × n g ; μ g and ΔU g are the generator reactive power balancing factor and the generator terminal voltage adjustment vector, respectively, both of which have a dimension of n g × 1; the i-th component of which is μ gi ; are the initial value, the lower limit and the upper limit of the generator reactive power output, respectively, all of which have a dimension of n g × 1; are the elements of the initial value, the lower limit and the upper limit of the generator reactive power output, respectively; C g is the sensitivity matrix of the generator reactive power output to the generator terminal voltage, which has a dimension of n g × n g , C gi is the i-th row of C g ; and ΔU g is the terminal voltage adjustment of the adjustable generator in the area.

[0031] The constraint conditions of the AC / DC coordinated two-level voltage control model M considering the correlation between the DC sending and receiving ends include the power flow constraint of the AC system, the power flow constraint of the converter node, the network security constraint of the AC / DC system, the converter characteristic equation constraint (1), the AC filter / parallel capacitor switching dead zone constraint of the converter bus reactive power, the sending-end converter station control variable constraint, and the receiving-end converter station control variable constraint.

[0032] The power flow constraint of the AC system is shown as follows:

[0033]

[0034] In the formula, P Gi Q Gi P represents the active and reactive power generated by the power source at AC node i, respectively; Li Q Li U represents the active and reactive power absorbed by the load at AC node i, respectively; i G represents the voltage at node i. ij B ij δ ij U represents the conductance, susceptance, and phase angle difference of line ij, respectively; i This represents the voltage at node j;

[0035] The power flow constraints of the converter node are as follows:

[0036]

[0037] In the formula, U d I is the voltage to ground at the DC terminal of the converter station. d d represents the current at the DC end of the converter station. ij The phase angle difference of the branch where the converter station is located; The power factor angle of the converter;

[0038] The network security constraints for AC / DC systems are as follows:

[0039] ΔU h =C h ΔU g (12)

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046] In the formula, △U h and The adjustment amount and maximum allowable value of the high-voltage bus voltage of the power plant are given, with dimension n. g ×1;C h This is the sensitivity matrix of the high-voltage bus voltage of the power plant to the generator terminal voltage, with dimension n. g ×ng ; and These represent the initial value, lower limit, and upper limit of the high-voltage bus voltage at the power plant, respectively, each with dimension n. g ×1; and These represent the initial value, lower limit, and upper limit of the central node voltage, respectively, each with dimension n. c ×1; and These represent the initial value, lower limit, and upper limit of the receiving-end converter bus node voltage, respectively, each with dimension n. dr ×1; and Let n represent the initial value, lower limit, and upper limit of the generator terminal voltage, respectively, each with dimension n. g ×1;C g This is the sensitivity matrix of the generator reactive power output to the generator terminal voltage; These are the initial value, lower limit, and upper limit vectors of the generator reactive power output, respectively;

[0047] The dead-time constraints for switching AC filters / parallel capacitors at the converter gate reactive power are shown below:

[0048]

[0049]

[0050]

[0051]

[0052] In the formula, C nd C nr These are the sensitivity matrices of reactive power at the converter station gates of the sending and receiving ends to the generator terminal voltage, respectively, with dimensions n. dd ×n g n dr ×n g ; These are the initial values ​​for reactive power exchanged at the converter gates at the sending and receiving ends, respectively, both with dimension n. dr ×1;Q dzd Q dzr The control dead zones of the AC filters / parallel capacitors at the converter gates of the sending and receiving ends are respectively, with dimensions n. dd ×1、n dr ×1; Let n be the initial values ​​of the reactive power compensation at the sending and receiving ends, respectively, with dimensions n. dd ×1、n dr ×1; Let n be the initial values ​​of the reactive power consumed by the sending and receiving end converters, respectively, with dimensions n. dd ×1、ndr ×1;n dd n dr These represent the number of converter station nodes in the DC near-area power grid at both the sending and receiving ends;

[0053] The control variable constraints for the sending-end converter station are as follows:

[0054]

[0055] In the formula, and Let n be the initial value, lower limit, and upper limit of the cosine of the firing angle of the sending-end converter, each with dimension n. dd ×1;C dd Let n be the sensitivity matrix of the converter firing angle cosine to the generator terminal voltage, with dimension n. dd ×n g ;

[0056] The control variable constraints for the receiving-end converter station are as follows:

[0057]

[0058] In the formula, and Let n be the initial value, lower limit, and upper limit of the no-load voltage on the valve side of the receiving-end converter transformer, each with dimension n. dr ×1;C dr Let n be the sensitivity matrix of the unloaded voltage on the valve side of the receiving-end converter transformer to the generator terminal voltage. dr ×n g .

[0059] The sensitivity matrix calculation steps in the AC / DC coordinated two-level voltage control model M, which considers the correlation between DC transmitters and receivers, include:

[0060] a) Establish the relationship between the injected reactive power ΔQ and the node voltage magnitude U in the case of a full Jacobian matrix, namely:

[0061]

[0062] In the formula, the subscripts L and G represent PQ nodes and PV nodes, respectively; the relation matrix A LL A LG A GL A GG The elements of matrix A; matrix ΔU L , ΔU G These represent the voltage amplitude adjustment amounts corresponding to the PQ node and PV node, respectively.

[0063] b) Calculate the sensitivity coefficient, i.e.:

[0064]

[0065]

[0066] In the formula, the superscript and subscript of the sensitivity coefficient matrix C correspond to the dependent variable and the independent variable, respectively; These represent the sensitivity coefficient matrices of the PQ node voltage amplitude and the PV node reactive power to the PV node voltage amplitude, respectively.

[0067] c) Substitute the converter characteristic equations (4)-(7) into equation (26) to calculate the state variable U of the receiving-end converter station. dr0 Q dr I d The sensitivity matrix to the generator terminal voltage adjustment, i.e.:

[0068]

[0069]

[0070]

[0071] In the formula, These are the sensitivity matrices of the unloaded voltage on the valve side of the receiving-end converter transformer, the reactive power consumed by the converter, and the DC current to the converter bus voltage, respectively, all of dimension n. dr ×n dr A diagonal matrix; C ir State variable I d Sensitivity matrix to generator terminal voltage adjustment;

[0072] Sensitivity matrix The diagonal elements are shown below:

[0073]

[0074]

[0075]

[0076] d) Establish the sensitivity matrix expression for the action constraints of discrete equipment in the sending-end converter station, i.e.:

[0077]

[0078]

[0079] In the formula, These are the control angle cosine values ​​of the converter at the sending-end converter station and the sensitivity matrices of the converter's reactive power consumption to DC current, respectively, both with dimension n.dd ×n dr A diagonal matrix; C ir The sensitivity matrix of DC current to the adjustable generator terminal voltage in the near-field area of ​​the receiving-end converter station is shown in equation (30).

[0080] Sensitivity matrix The diagonal elements are shown below:

[0081]

[0082]

[0083] 3) Perform quadratic programming to solve the AC / DC coordinated two-stage voltage control model M that considers the correlation between DC sending and receiving ends, and obtain the AC / DC system coordinated two-stage voltage control mode.

[0084] Tools for solving the AC / DC coordinated two-stage voltage control model M that considers the DC-DC transmission-receiver correlation include CPLEX.

[0085] The technical effects of this invention are undeniable. In response to the insufficient reactive power support capacity of the receiving-end power grid in DC projects, and the safety hazards of the high frequency of operation of discrete equipment in existing converter stations affecting equipment lifespan, this invention can coordinate the reactive power output of DC near-field generators in the receiving-end power grid, while taking into account the dynamic reactive power reserve level of the DC near-field, strengthening the control of the voltage level of the receiving-end power grid, and improving the stability of the safe operation of the power grid.

[0086] Meanwhile, previous studies did not consider the voltage-reactive power correlation between the sending and receiving end converter stations under typical DC control modes, which may have resulted in control effects that differed significantly from actual conditions. This invention derives a quantitative formula for the voltage-reactive power correlation between the sending and receiving ends based on a specific expression of the converter station's voltage-reactive power characteristics under typical DC control modes, and incorporates this formula into the receiving end's near-field coordinated two-stage voltage control strategy. By adding constraints on the actions of discrete equipment at the sending end converter station to the constraints, the risk of additional actions by discrete equipment at the sending end converter station due to the receiving end implementing the control strategy is reduced, and the control effect is more closely aligned with engineering practice. Attached Figure Description

[0087] Figure 1 An equivalent model of an ultra-high voltage direct current converter station;

[0088] Figure 2 This is the topology diagram of the receiving end IEEE 39-node system. Detailed Implementation

[0089] The present invention will be further described below with reference to embodiments, but it should not be construed that the scope of the present invention is limited to the following embodiments. Various substitutions and modifications made based on ordinary technical knowledge and common practices in the art without departing from the above-described technical concept of the present invention should be included within the scope of protection of the present invention.

[0090] Example 1:

[0091] See Figure 1 and Figure 2 A coordinated two-stage voltage control method for AC / DC systems considering DC control mode includes the following steps:

[0092] 1) Establish the external characteristic equations of the rectifier station and inverter station connected to the AC system, and determine the partial derivatives of the active power transmitted and reactive power consumed by the converter stations on both sides with respect to the voltage amplitude of the converter bus.

[0093] The steps for establishing the external characteristic equations of the rectifier station and inverter station connected to the AC system, and determining the partial derivatives of the active power transmitted and reactive power consumed by the converter stations on both sides with respect to the voltage amplitude of the converter bus, include:

[0094] 1.1) Establish the characteristic equations for the sending and receiving end converters, i.e.:

[0095]

[0096] In the formula, α is the trigger angle, γ is the turn-off angle; N d N r The number of six-pulse converters per pole at the sending and receiving ends, respectively; k pd k pr These represent the number of operating poles of the sending and receiving end converters, respectively; T d =U dd0B / U ddB T r =U dr0B / U drB These are the conversion coefficients for the sending and receiving end reference values, respectively; U dd0B U ddB These are the valve-side reference voltage and DC reference voltage of the sending-end converter transformer, respectively. dr0B U drB These are the valve-side reference voltage and DC reference voltage of the receiving-end converter transformer, respectively; Q dd Q dr The reactive power consumed by the sending and receiving end converters are respectively; P dd P dr These represent the active power consumed by the sending and receiving end converters, respectively; I d U is the current at the DC end of the converter station. td U tr These are the converter bus node voltages at the sending and receiving ends, respectively; k Tdk Tr These are the transformer turns ratios of the sending and receiving end converter stations, respectively; X d X r These are the equivalent reactances of the converter transformers at the sending and receiving ends of the converter stations, respectively; R d This is the equivalent resistance of a DC transmission line. U dd0 U dd These are the valve-side voltage and DC voltage of the sending-end converter transformer, respectively; U dr0 U dr These are the valve-side voltage and DC voltage of the receiving-end converter transformer, respectively.

[0097] 1.2) When the DC system does not inject power into the AC system, establish the steady-state power flow equations for the pure AC system, i.e.:

[0098]

[0099] In the formula, △P and △Q are the imbalance matrices of active and reactive power of the AC bus, respectively; △δ and △U are the correction matrices of phase angle and amplitude of AC bus voltage, respectively; J Pδ J PU J Qδ J QU These are the four corresponding submatrices of the Jacobian matrix J.

[0100] 1.3) When a DC system supplies power to an AC system, the submatrix J in the Jacobian matrix J... PU J QU The diagonal elements are corrected, and the corrected element J PU '、Element J QU As shown in the following formula:

[0101]

[0102] Where, when node i is the sending-end converter bus node, s i =1; when node i is the receiving-end converter bus node, s i =-1; U i P is the voltage at node i; dci Q dci Let i be the active power and reactive power of DC node i.

[0103] 1.4) Establish the control equations for the sender and receiver converter station controllers, namely:

[0104]

[0105] In the formula, P dd γ is the DC power; γ is the inverter station turn-off angle; P dd sp γ spThese are the planned values ​​for DC transmission power and inverter station turn-off angle.

[0106] 1.5) Establish the external characteristic equations of the rectifier station and inverter station connected to the AC system, namely:

[0107]

[0108] The partial derivatives of the active power transmitted and reactive power consumed by the two converter stations with respect to the voltage amplitude of the converter bus are as follows:

[0109]

[0110] In the formula, D d D r To calculate the relevant parameters of the DC state variables at the sending and receiving ends; The partial derivative of reactive power consumed by the sending-end converter station with respect to the voltage of the receiving-end converter bus;

[0111] Among them, the partial derivative of the DC current with respect to the amplitude of the receiving-end converter bus voltage. As shown below:

[0112]

[0113] 2) Based on the external characteristic equations of the rectifier station and inverter station connected to the AC system, a coordinated AC / DC two-stage voltage control model M considering the correlation between the DC transmitting and receiving ends is established;

[0114] The objective function of the AC / DC coordinated two-stage voltage control model M, which considers the correlation between DC transmitters and receivers, is shown below:

[0115]

[0116]

[0117] In the formula, W c W t and W q As the weight, and W c >W q W t >W q ; and These are the initial value and ideal reference value of the voltage vector at the central node, respectively, both with dimension n. c ×1; and These are the initial value and the set reference value of the voltage vector at the receiving-end converter bus node, respectively, both with dimension n. dr ×1;n c n g and n drThese represent the number of AC central nodes, controlled power plant nodes, and converter station nodes at the receiving end of the power grid, respectively; C c C t These are the sensitivity matrices of the central node and converter bus node voltages to the generator terminal voltage, respectively, with dimensions n. c ×n g n dr ×n g μ g and ΔU g These are the generator reactive power balancing factor and the generator terminal voltage regulation vector, respectively, both with dimension n. g ×1; where the i-th component is μ gi ; These are the initial value, lower limit, and upper limit vectors of the generator reactive power output, each with dimension n. g ×1; These are the elements of the generator reactive power output initial value, lower limit, and upper limit vector, respectively; C g Let n be the sensitivity matrix of the generator reactive power output to the generator terminal voltage. g ×n g C gi C g The i-th row; ΔU g This refers to the adjustment amount of the generator terminal voltage of the adjustable generator within the area.

[0118] The constraints of the AC / DC coordinated two-level voltage control model M considering the correlation between DC sending and receiving ends include the power flow constraints of the AC system, the power flow constraints of the converter nodes, the network security constraints of the AC / DC system, the characteristic equation constraints of the sending and receiving end converters (1), the dead zone constraints of the AC filter / parallel capacitor switching of the reactive power at the converter gate, the control variable constraints of the sending end converter station, and the control variable constraints of the receiving end converter station.

[0119] The power flow constraints of the communication system are as follows:

[0120]

[0121] In the formula, P Gi Q Gi P represents the active and reactive power generated by the power source at AC node i, respectively; Li Q Li U represents the active and reactive power absorbed by the load at AC node i, respectively; i G represents the voltage at node i. ij B ij δ ij U represents the conductance, susceptance, and phase angle difference of line ij, respectively; i This represents the voltage at node j;

[0122] The power flow constraints of the converter node are as follows:

[0123]

[0124] In the formula, U d I is the voltage to ground at the DC terminal of the converter station. d d represents the current at the DC end of the converter station. ij The phase angle difference of the branch where the converter station is located; The power factor angle of the converter;

[0125] The network security constraints for AC / DC systems are as follows:

[0126] ΔU h =C h ΔU g (12)

[0127]

[0128]

[0129]

[0130]

[0131]

[0132]

[0133] In the formula, △U h and The adjustment amount and maximum allowable value of the high-voltage bus voltage of the power plant are given, with dimension n. g ×1;C h This is the sensitivity matrix of the high-voltage bus voltage of the power plant to the generator terminal voltage, with dimension n. g ×n g ; and These represent the initial value, lower limit, and upper limit of the high-voltage bus voltage at the power plant, respectively, each with dimension n. g ×1; and These represent the initial value, lower limit, and upper limit of the central node voltage, respectively, each with dimension n. c ×1; and These represent the initial value, lower limit, and upper limit of the receiving-end converter bus node voltage, respectively, each with dimension n. dr ×1; and Let n represent the initial value, lower limit, and upper limit of the generator terminal voltage, respectively, each with dimension n. g ×1;C gThis is the sensitivity matrix of the generator reactive power output to the generator terminal voltage; These are the initial value, lower limit, and upper limit vectors of the generator reactive power output, respectively;

[0134] The dead-time constraints for switching AC filters / parallel capacitors at the converter gate reactive power are shown below:

[0135]

[0136]

[0137]

[0138]

[0139] In the formula, C nd C nr These are the sensitivity matrices of reactive power at the converter station gates of the sending and receiving ends to the generator terminal voltage, respectively, with dimensions n. dd ×n g n dr ×n g ; These are the initial values ​​for reactive power exchanged at the converter gates at the sending and receiving ends, respectively, both with dimension n. dr ×1;Q dzd Q dzr The control dead zones of the AC filters / parallel capacitors at the converter gates of the sending and receiving ends are respectively, with dimensions n. dd ×1、n dr ×1; Let n be the initial values ​​of the reactive power compensation at the sending and receiving ends, respectively, with dimensions n. dd ×1、n dr ×1; Let n be the initial values ​​of the reactive power consumed by the sending and receiving end converters, respectively, with dimensions n. dd ×1、n dr ×1;n dd n dr These represent the number of converter station nodes in the DC near-area power grid at both the sending and receiving ends;

[0140] The control variable constraints for the sending-end converter station are as follows:

[0141]

[0142] In the formula, and Let n be the initial value, lower limit, and upper limit of the cosine of the firing angle of the sending-end converter, each with dimension n. dd ×1;C dd Let n be the sensitivity matrix of the converter firing angle cosine to the generator terminal voltage, with dimension n. dd ×ng ;

[0143] The control variable constraints for the receiving-end converter station are as follows:

[0144]

[0145] In the formula, and Let n be the initial value, lower limit, and upper limit of the no-load voltage on the valve side of the receiving-end converter transformer, each with dimension n. dr ×1;C dr Let n be the sensitivity matrix of the unloaded voltage on the valve side of the receiving-end converter transformer to the generator terminal voltage. dr ×n g .

[0146] The sensitivity matrix calculation steps in the AC / DC coordinated two-level voltage control model M, which considers the correlation between DC transmitters and receivers, include:

[0147] a) Establish the relationship between the injected reactive power ΔQ and the node voltage magnitude U in the case of a full Jacobian matrix, namely:

[0148]

[0149] In the formula, the subscripts L and G represent PQ nodes and PV nodes, respectively; the relation matrix A LL A LG A GL A GG The elements of matrix A; matrix ΔU L , ΔU G These represent the voltage amplitude adjustment amounts corresponding to the PQ node and PV node, respectively.

[0150] b) Calculate the sensitivity coefficient, i.e.:

[0151]

[0152]

[0153] In the formula, the superscript and subscript of the sensitivity coefficient matrix C correspond to the dependent variable and the independent variable, respectively; These represent the sensitivity coefficient matrices of the PQ node voltage amplitude and the PV node reactive power to the PV node voltage amplitude, respectively.

[0154] c) Substitute the converter characteristic equations (4)-(7) into equation (26) to calculate the state variable U of the receiving-end converter station. dr0 Q dr I dThe sensitivity matrix to the generator terminal voltage adjustment, i.e.:

[0155]

[0156]

[0157]

[0158] In the formula, These are the sensitivity matrices of the unloaded voltage on the valve side of the receiving-end converter transformer, the reactive power consumed by the converter, and the DC current to the converter bus voltage, respectively, all of dimension n. dr ×n dr A diagonal matrix; C ir State variable I d Sensitivity matrix to generator terminal voltage adjustment;

[0159] Sensitivity matrix The diagonal elements are shown below:

[0160]

[0161]

[0162]

[0163] d) Establish the sensitivity matrix expression for the action constraints of discrete equipment in the sending-end converter station, i.e.:

[0164]

[0165]

[0166] In the formula, These are the control angle cosine values ​​of the converter at the sending-end converter station and the sensitivity matrices of the converter's reactive power consumption to DC current, respectively, both with dimension n. dd ×n dr A diagonal matrix; C ir The sensitivity matrix of DC current to the adjustable generator terminal voltage in the near-field area of ​​the receiving-end converter station is shown in equation (30).

[0167] Sensitivity matrix The diagonal elements are shown below:

[0168]

[0169]

[0170] 3) Perform quadratic programming to solve the AC / DC coordinated two-stage voltage control model M that considers the correlation between DC sending and receiving ends, and obtain the AC / DC system coordinated two-stage voltage control mode.

[0171] Tools for solving the AC / DC coordinated two-stage voltage control model M that considers the DC-DC transmission-receiver correlation include CPLEX.

[0172] This invention takes into account the voltage and reactive power correlation between the converter stations at the sending and receiving ends under typical DC control mode, namely, constant power at the sending end and constant control angle at the receiving end, and establishes a more accurate voltage and reactive power characteristic model for the converter stations on both sides of the sending and receiving ends.

[0173] The impact of the correlation between the sending and receiving converter stations on the secondary voltage control of the DC near-field coordination at the receiving end was considered. The risk that the receiving end control measures may bring additional switching to the discrete equipment of the sending end converter station was taken into account, and the action constraints of the discrete equipment of the sending and receiving end converter stations under the correlation were added.

[0174] The characteristics of different types of nodes were fully considered when solving the sensitivity of relevant parameters in AC / DC systems. Based on the important transitivity of DC state variables between voltage and reactive power state parameters of the sending and receiving converter stations, the formula for solving the relevant sensitivity coefficient matrix of the sending and receiving converter stations was derived.

[0175] To address the weak reactive power support of the receiving-end power grid, the control objectives incorporate voltage control requirements for the central node and converter bus node, and also include a control requirement for the reactive power output balance of DC near-field generators. By flexibly adjusting the various target coefficients, an optimal control scheme can be obtained by coordinating voltage control and reactive power margin in the receiving-end DC near-field power grid. This significantly improves the voltage safety level at the receiving end, ensures a certain reactive power reserve capacity, and enhances system stability.

[0176] Example 2:

[0177] The coordinated two-stage voltage control method for AC / DC systems considering the correlation between DC transmitters and receivers mainly includes the following steps:

[0178] 1) The voltage-reactive characteristics of the converter prove that there is a correlation between the sending and receiving ends of DC under the control mode of constant power at the sending end and constant control angle at the receiving end;

[0179] The per-unit form of the characteristic equations for the sending and receiving end converters is shown below:

[0180]

[0181] Where α is the trigger angle and γ is the turn-off angle; N d N r The number of six-pulse converters per pole at the sending and receiving ends are respectively taken as 4 in this paper; k pd k prThese represent the number of operating poles of the sending and receiving end converters, respectively; T d T r These are the conversion coefficients for the sending and receiving end reference values, respectively, with T... d =U dd0B / U ddB T r =U dr0B / U drB U dd0B U ddB These are the valve-side reference voltage and DC reference voltage of the sending-end converter transformer, respectively. dr0B U drB These are the valve-side reference voltage and DC reference voltage of the receiving-end converter transformer, respectively; Q dd Q dr The reactive power consumed by the sending and receiving end converters are respectively.

[0182] When the DC system does not inject power into the AC system, the steady-state power flow equation of the pure AC system is:

[0183]

[0184] Where △P and △Q are the imbalance matrices of active and reactive power of the AC bus, respectively; △δ and △U are the correction matrices of phase angle and amplitude of AC bus voltage, respectively; J Pδ J PU J Qδ J QU These are the four corresponding submatrices of the Jacobian matrix J.

[0185] When a DC system supplies power to an AC system, considering the specific voltage and reactive power characteristics of the converter stations on both sides, i.e., the active and reactive power transmitted by the converter stations will be affected by the amplitude of the converter bus voltage, it is necessary to determine the submatrix J in its Jacobian matrix J. PU J QU The diagonal elements are corrected, resulting in J. PU '、J QU As shown in the following formula:

[0186]

[0187] Where, when node i is the sending-end converter bus node, s i =1; when node i is the receiving-end converter bus node, s i =-1.

[0188] Correction elements It needs to be obtained based on the external characteristic equations of the converter under different control modes. Under the constant power at the sending end and constant control angle at the receiving end (CP-CEA) control mode, the sender and receiver converter station controllers adjust the DC power P according to the given instructions.dd Keep as P dd sp The inverter station's turn-off angle γ is kept constant, while the turn-off angle γ is maintained at γ. sp The governing equations are as follows:

[0189]

[0190] At this point, the external characteristic equations of the rectifier station and inverter station connected to the AC system can be described as follows:

[0191]

[0192] Therefore, the partial derivatives of the active power transmitted and reactive power consumed by the two converter stations with respect to the converter bus voltage amplitude can be obtained as follows:

[0193]

[0194] in, The partial derivative of reactive power consumed by the sending-end converter station with respect to the voltage of the receiving-end converter bus; The partial derivative of the DC current with respect to the magnitude of the receiving-end converter bus voltage is given by the following formula:

[0195]

[0196] From equations (5) and (7), it can be seen that the amplitude of the DC current under CP-CEA control mode is only related to the voltage fluctuation of the receiving-end converter bus. Therefore, the following conclusion can be drawn from equation (6): the reactive power consumption of the sending-end converter station is affected by the voltage of the converter buses on both sides, while the reactive power consumption of the receiving-end converter station is only related to the voltage of the converter bus on that side.

[0197] 2) To address the correlation between the DC transmitting and receiving ends, a coordinated AC / DC two-stage voltage control model M was established, taking into account the correlation between the DC transmitting and receiving ends.

[0198] 2.1) Set the optimization objective function

[0199] With the objectives of minimizing the voltage deviation between the central node and the converter bus node, and balancing the reactive power output of generators within the region, the objective function is specifically:

[0200]

[0201]

[0202] In the formula, the number of AC central nodes of the receiving-end power grid, the number of controlled power plant nodes, and the number of converter station nodes are n, respectively. c n g and n dr In equations (8)-(9), W c Wt and W q The weights for the three objectives are given based on expert experience and have W. c W c >W q U c 0 and U c ref These are the initial value and ideal reference value of the voltage vector at the central node, respectively, both with dimension n. c ×1; U tr 0 and U tr set These are the initial value and the set reference value of the voltage vector at the receiving-end converter bus node, respectively, both with dimension n. dr ×1;C c C t These are the sensitivity matrices of the central node and converter bus node voltages to the generator terminal voltage, respectively, with dimensions n. c ×n g n dr ×n g μ g and ΔU g These are the generator reactive power balancing factor and the generator terminal voltage regulation vector, respectively, both with dimension n. g ×1; where the i-th component is μ gi Q g 0 Q g min Q g max and are the initial value, lower limit, and upper limit vectors of the generator's reactive power output, respectively, all with dimension n. g ×1;C g Let n be the sensitivity matrix of the generator reactive power output to the generator terminal voltage. g ×n g C gi C g The i-th row.

[0203] 2.2) Set constraints

[0204] The constraints include not only the power flow constraints and network security constraints of the AC / DC system, but also the control capability constraints of the generator, the control capability constraints of the receiving-end converter, and the state variable constraints of the converter station gate coupling. In addition, they also include the control capability constraints of the sending-end converter and the state variable constraints of the converter station gate coupling.

[0205] ① Power flow constraints of the communication system

[0206]

[0207] In the formula, P Gi Q Gi P represents the active and reactive power generated by the power source at AC node i, respectively; Li Q Li U represents the active and reactive power absorbed by the load at AC node i, respectively; i G represents the voltage at node i. ij B ij δ ij U represents the conductance, susceptance, and phase angle difference of line ij, respectively; i This represents the voltage at node i.

[0208] ② Power flow constraints at converter nodes

[0209]

[0210] In the formula, U d I is the voltage to ground at the DC terminal of the converter station. d d represents the current at the DC end of the converter station. ij The phase angle difference of the branch where the converter station is located; The power factor angle of the converter.

[0211] ③ Network security constraints of AC / DC systems

[0212] Within the control area, the voltage of the generator high-voltage side bus, the voltage of the central point and the converter bus all meet the upper and lower limits of their voltage constraints. At the same time, the single-step adjustment of the voltage of the power plant high-voltage side bus, the generator terminal voltage and reactive power output also need to meet the upper and lower limits of their constraints.

[0213] ΔU h =C h ΔU g (12)

[0214]

[0215]

[0216]

[0217]

[0218]

[0219]

[0220] In the formula, △U h and △U h max The adjustment amount and maximum allowable value of the high-voltage bus voltage of the power plant are given, with dimension n. g×1;C h This is the sensitivity matrix of the high-voltage bus voltage of the power plant to the generator terminal voltage, with dimension n. g ×n g U h 0 U h min and U h max These represent the initial value, lower limit, and upper limit of the high-voltage bus voltage at the power plant, respectively, each with dimension n. g ×1; U c min and U c max These represent the lower and upper limits of the central node voltage, respectively, both with dimension n. c ×1; U tr min and U tr max These represent the lower and upper limits of the receiving-end converter bus node voltage, respectively, both with dimension n. dr ×1; U g 0 U g min and U g max Let n represent the initial value, lower limit, and upper limit of the generator terminal voltage, respectively, each with dimension n. g ×1.

[0221] ④ The characteristic equations of the sending and receiving end converters are constrained as shown in equation (1).

[0222] ⑤ Dead-zone constraint for switching reactive power AC filters / parallel capacitors at the converter gate

[0223] Since AC filters and parallel capacitors are discrete regulating devices, the ideal state of "zero reactive power exchange" cannot be guaranteed at all times. Assume that the converter stations at both ends adopt reactive power control mode. In this mode, when the reactive power exchanged at the converter gate exceeds the dead-zone regulation range of its single AC filter / parallel capacitor, the AC filter / parallel capacitor needs to operate. Therefore, in secondary voltage control, to avoid additional operation of the AC filter / parallel capacitor, the dead-zone constraint of AC filter / parallel capacitor switching needs to be considered.

[0224]

[0225]

[0226]

[0227]

[0228] In the formula, Cnd C nr These are the sensitivity matrices of reactive power at the converter station gates of the sending and receiving ends to the generator terminal voltage, respectively, with dimensions n. dd ×n g n dr ×n g Q exd 0 Q exr 0 These are the initial values ​​for reactive power exchanged at the converter gates at the sending and receiving ends, respectively, both with dimension n. dr ×1;Q dzd Q dzr The control dead zones of the AC filters / parallel capacitors at the converter gates of the sending and receiving ends are respectively, with dimensions n. dd ×1、n dr ×1;Q fd 0 Q fr 0 Let n be the initial values ​​of the reactive power compensation at the sending and receiving ends, respectively, with dimensions n. dd ×1、n dr ×1;Q dd 0 Q dr 0 Let n be the initial values ​​of the reactive power consumed by the sending and receiving end converters, respectively, with dimensions n. dd ×1、n dr ×1.

[0229] ⑥ Control variable constraints of the sending-end converter station

[0230] Under CP-CEA control, the sending-end converter transformer uses angle control. Furthermore, the optimized adjustment of the receiving-end converter bus voltage primarily affects the converter control angle α and the reactive power Q consumed by the converter within the sending-end converter station. dd This could have an impact, potentially causing additional actions on the discrete equipment of the sending-end converter station. Therefore, this paper incorporates control angle safety operation constraints for the sending-end converter station and dead-zone constraints for the switching of AC filters / parallel capacitors at the converter gate into the model.

[0231]

[0232] In the formula, the number of converter station nodes in the sending-end DC near-area power grid is n. dd cosα 0 cosα min and cosα max Let n be the initial value, lower limit, and upper limit of the cosine of the firing angle of the sending-end converter, each with dimension n. dd ×1;C dd Let n be the sensitivity matrix of the converter firing angle cosine to the generator terminal voltage, with dimension n.dd ×n g .

[0233] ⑤ Control variable constraints at the receiving-end converter station

[0234] In DC CP-CEA control mode, the receiver-end converter transformer is voltage-controlled. That is, when the converter bus voltage changes, the adjustment of the converter transformer taps is mainly relied upon to maintain the unloaded voltage U on the valve side of the receiver-end converter transformer. dr0 Maintaining it within the safe operating range. Therefore, in secondary voltage control, to avoid additional operation of the converter transformer, U needs to be considered. dr0 Changing safety operation constraints:

[0235]

[0236] In the formula, U dr0 0 U dr0 min and U dr0 max Let n be the initial value, lower limit, and upper limit of the no-load voltage on the valve side of the receiving-end converter transformer, each with dimension n. dr ×1. C dr Let n be the sensitivity matrix of the unloaded voltage on the valve side of the receiving-end converter transformer to the generator terminal voltage. dr ×n g .

[0237] 2.3) Sensitivity matrix calculation

[0238] Since the DC system is not approximated, the calculation of the sensitivity coefficient needs to consider the specific voltage and reactive power characteristics of the converter station, and the Jacobian matrix elements will be corrected. When the AC system transmits power to the DC system, the DC converter station affects the AC system through the converter bus node. As shown in equation (3), the diagonal elements of the Jacobian matrix J need to be corrected. Under the CP-CEA control mode, the corrected element is J. PU '、J QU The expressions are shown in equations (6) and (7). Assuming that the active power injected into the node remains constant, i.e., ΔP = 0, the relationship between the reactive power injected into the node ΔQ and the node voltage amplitude U under the full Jacobian matrix is ​​as follows:

[0239]

[0240] In the formula, the subscripts L and G represent PQ nodes and PV nodes, respectively.

[0241] Regarding control variables, different types of nodes have different assumptions: for a PQ node, if P and Q are adjustable, then there is a control variable ΔU. G=0, meaning the node voltage is not adjustable; similarly, the U of a PV node is adjustable with ΔQ. L =0. Therefore, according to equation (25), the required sensitivity coefficient can be obtained as follows:

[0242]

[0243]

[0244] In the formula, the superscript and subscript of the sensitivity coefficient matrix C correspond to the dependent variable and the independent variable, respectively. Equations (26) and (27) represent the sensitivity coefficient matrices of the voltage amplitude of the PQ node and the reactive power of the PV node to the voltage amplitude of the PV node, respectively.

[0245] Due to the voltage U at the receiving-end converter bus node tr It is a function of the converter state variables. Substituting the converter characteristic equations (4)-(7) into equation (26), we can solve for the receiving-end converter station state variable U in equations (24) and (19). dr0 Q dr I d The sensitivity matrix for the generator terminal voltage adjustment is expressed as follows:

[0246]

[0247]

[0248]

[0249] In the formula, C Utr Udr0 C Utr Qdr C Utr Id These are the sensitivity matrices of the unloaded voltage on the valve side of the receiving-end converter transformer, the reactive power consumed by the converter, and the DC current to the converter bus voltage, respectively, all of dimension n. dr ×n dr The diagonal matrix is ​​given by equations (31)-(33).

[0250]

[0251]

[0252]

[0253] Under CP-CEA control mode, the receiving-end converter station uses DC current I dThis has an impact on the sending-end converter station. From equations (4)-(7) and (32), the sensitivity matrix expression in the discrete equipment action constraints of the sending-end converter station can be obtained as follows:

[0254]

[0255]

[0256] In the formula, C Id cosα C Id Qdd These are the control angle cosine values ​​of the converter at the sending-end converter station and the sensitivity matrices of the converter's reactive power consumption to DC current, respectively, both with dimension n. dd ×n dr The diagonal matrix has the following expression for its diagonal elements:

[0257]

[0258]

[0259] 3) Solve the AC / DC coordinated two-stage voltage control model M, which considers the correlation between DC transmitters and receivers, using quadratic programming.

[0260] 3.1) Solution Steps

[0261] Model M is a multi-objective linear quadratic programming problem, which can be solved using CPLEX. The specific process is as follows:

[0262] Perform power flow calculations for AC / DC systems;

[0263] The coefficients of the relevant sensitivity matrix in the objective function and constraints can be obtained from the sensitivity calculation formula.

[0264] The CPLEX toolkit is called through the yalmip toolbox in the Matlab software platform to solve the problem.

[0265] Example 3:

[0266] For a domestic UHVDC receiving-end converter station, coordinated two-stage voltage control is implemented based on its typical daily DC transmission power plan. Considering the correlation between the DC sending and receiving ends, the coordinated two-stage voltage control of the AC / DC system mainly includes the following steps:

[0267] 1) Main steps

[0268] ① Select the UHVDC transmitting and receiving end converter station, its equivalent model is as follows: Figure 1 As shown, the AC power grid of the converter station is modeled on an equivalent basis based on the IEEE 39-bus system, and the planned DC transmission power curve of a typical day of the converter station and its equivalent power source prediction curve are selected.

[0269] ② Construct a coordinated two-stage voltage control model for AC / DC systems, considering the correlation between DC sending and receiving ends, as shown in equations (8)-(24), and solve it using the algorithm described above.

[0270] 2) Model control effect analysis

[0271] The AC / DC system coordinated two-level voltage control model considering the correlation between DC sending and receiving ends is mainly reflected in the number of actions of discrete control equipment in the converter station, the voltage fluctuations of the central node and the converter node, and the reactive power balance of the generator. In order to verify the effectiveness of the model M of this invention, the following comparative experiment is designed for a single time section:

[0272] Option 1: Model M in this paper;

[0273] Option 2: Based on model M, without considering the dead zone constraint for switching AC filters at the sending-end converter station and the safe operation constraint for converter control angle;

[0274] Through simulation, the optimization results of the two control schemes can be obtained in a single time segment.

[0275] The simulation results of Scheme 1 and Scheme 2 for a single time section are shown in Table 1.

[0276] Table 1 Optimization results for a single time short surface

[0277]

[0278] Note: In this definition, the positive direction of reactive power exchange at the converter gate is from the AC system to the DC system.

[0279] As shown in Table 1, Scheme 1, considering the correlation between the sending and receiving ends under the DC sending-end constant power and receiving-end constant control angle control mode, adds additional action constraints to the discrete equipment of the sending-end converter station. Therefore, under Scheme 1, no additional actions occur in the discrete equipment of the sending and receiving end converter stations. Scheme 2 has a reactive power exchange rate of -611 MVar at the sending-end converter gate, while the dead zone for switching the parallel capacitors at the sending-end converter gate is 300 MVar. Therefore, under this scheme, the reactive power exchange rate at the sending-end converter gate exceeds 103.7% of the dead zone for switching the parallel capacitors at the sending-end converter station, which will cause additional actions to occur in the discrete equipment of the sending-end converter station.

[0280] Simulation results show that Scheme 1, i.e., Model M of this invention, can significantly reduce the risk of additional switching of discrete equipment in the sending-end converter station due to the control behavior of the receiving end, and reduce the number of adjustments of discrete equipment in the converter station, under actual operating conditions where there is correlation between the sending and receiving end converter stations. Model M of this invention is better suited for automatic voltage control of AC / DC systems.

Claims

1. A coordinated two-stage voltage control method for AC / DC systems considering DC control, characterized in that, Includes the following steps: 1) Establish the external characteristic equations of the rectifier station and inverter station connected to the AC system, and determine the partial derivatives of the active power transmitted and reactive power consumed by the converter stations on both sides with respect to the voltage amplitude of the converter bus. 2) Based on the external characteristic equations of the rectifier station and inverter station connected to the AC system, a coordinated AC / DC two-stage voltage control model M considering the correlation between the DC transmitting and receiving ends is established; 3) Perform quadratic programming to solve the AC / DC coordinated two-stage voltage control model M that considers the correlation between DC sending and receiving ends, and obtain the AC / DC system coordinated two-stage voltage control mode; The sensitivity matrix calculation steps in the AC / DC coordinated two-level voltage control model M, which considers the correlation between DC transmitters and receivers, include: s1) Establish the relationship between the node-injected reactive power ΔQ and the node voltage magnitude U in the case of a full Jacobian matrix, namely: In the formula, the subscripts L and G represent PQ nodes and PV nodes, respectively; the relation matrix A LL A LG A GL A GG The elements of matrix A; matrix ΔU L , ΔU G These represent the voltage amplitude adjustment amounts corresponding to the PQ and PV nodes, respectively; J Pδ J Qδ The corresponding submatrix of the Jacobian matrix J; J PU '、J QU 'For the submatrix J in the Jacobian matrix J PU J QU The elements after correcting the diagonal elements; s2) Calculate the sensitivity coefficient, i.e.: In the formula, the superscript and subscript of the sensitivity coefficient matrix C correspond to the dependent variable and the independent variable, respectively; These represent the sensitivity coefficient matrices of the PQ node voltage amplitude and the PV node reactive power to the PV node voltage amplitude, respectively. s3) Substitute the converter characteristic equations (4)-(7) into equation (26) to calculate the state variable U of the receiving-end converter station. dr0 Q dr I d The sensitivity matrix to the generator terminal voltage adjustment, i.e.: In the formula, These are the sensitivity matrices of the unloaded voltage on the valve side of the receiving-end converter transformer, the reactive power consumed by the converter, and the DC current to the converter bus voltage, respectively, all of dimension n. dr ×n dr A diagonal matrix; C ir C represents the sensitivity matrix of DC current to the adjustable generator terminal voltage in the near-field zone of the receiving-end converter station; dr C represents the sensitivity matrix of the unloaded voltage on the valve side of the receiving-end converter transformer to the generator terminal voltage. nr The sensitivity matrix of reactive power at the receiving-end converter station gate to generator terminal voltage; Sensitivity matrix The diagonal elements are shown below: In the formula, N d N r The number of six-pulse converters per pole at the sending and receiving ends, respectively; k Tr R is the transformer ratio of the converter transformer at the receiving end converter station. d X is the equivalent resistance of a DC transmission line; d X r These are the equivalent reactances of the converter transformers at the sending and receiving ends of the converter stations, respectively; T r =U dr0B / U drB U is the conversion factor for the receiving end reference value; dr0B U drB These represent the valve-side reference voltage and DC reference voltage of the receiving-end converter transformer, respectively; γ is the turn-off angle; T d =U dd0B / U ddB U dd0B U ddB These are the valve-side reference voltage and DC reference voltage of the sending-end converter transformer, respectively; U dd0 U dd These are the valve-side voltage and DC voltage of the sending-end converter transformer, respectively; U dr0 U dr These are the valve-side voltage and DC voltage of the receiving-end converter transformer, respectively; P dd The active power consumed by the sending-end converter; I d This refers to the current at the DC end of the converter station; The converter characteristic equations (4)-(7) are shown below: In the formula, P dd The active power consumed by the sending-end converter; γ is the inverter station turn-off angle; γ sp The planned values ​​for the active power consumed by the sending-end converter and the inverter station turn-off angle; In the formula, D d D r To calculate the relevant parameters of the DC state variables at the sending and receiving ends; The partial derivative of the reactive power consumed by the sending-end converter station with respect to the voltage of the receiving-end converter bus; k Td k Tr These represent the transformer turns ratios of the sending and receiving end converter stations, respectively; T d =U dd0B / U ddB T r =U dr0B / U drB These are the conversion coefficients for the sending and receiving end reference values, respectively; U dd0B U ddB These are the valve-side reference voltage and DC reference voltage of the sending-end converter transformer, respectively. dr0B U drB These are the valve-side reference voltage and DC reference voltage of the receiving-end converter transformer, respectively; U td U tr These are the converter bus node voltages at the sending and receiving ends, respectively; Q dd Q dr The reactive power consumed by the sending and receiving end converters are respectively; P dd P dr These represent the active power consumed by the sending and receiving end converters, respectively; I d This refers to the current at the DC end of the converter station; s4) Establish the sensitivity matrix expression in the action constraints of discrete equipment in the sending-end converter station, that is: In the formula, These are the control angle cosine values ​​of the converter at the sending-end converter station and the sensitivity matrices of the converter's reactive power consumption to DC current, respectively, both with dimension n. dd ×n dr A diagonal matrix; C ir C represents the sensitivity matrix of DC current to the adjustable generator terminal voltage in the near-field zone of the receiving-end converter station; dd C is the sensitivity matrix of the converter firing angle cosine to the generator terminal voltage; nd The sensitivity matrix of reactive power at the sending-end converter station gate to generator terminal voltage; Sensitivity matrix The diagonal elements are shown below:

2. The AC / DC system coordinated two-stage voltage control method considering DC control mode according to claim 1, characterized in that, The steps for establishing the external characteristic equations of the rectifier station and inverter station connected to the AC system, and determining the partial derivatives of the active power transmitted and reactive power consumed by the converter stations on both sides with respect to the voltage amplitude of the converter bus, include: 1) Establish the characteristic equations for the sending and receiving end converters, namely: In the formula, α is the trigger angle, γ is the turn-off angle; N d N r The number of six-pulse converters per pole at the sending and receiving ends, respectively; k pd k pr These represent the number of operating poles of the sending and receiving end converters, respectively; T d =U dd0B / U ddB T r =U dr0B / U drB These are the conversion coefficients for the sending and receiving end reference values, respectively; U dd0B U ddB These are the valve-side reference voltage and DC reference voltage of the sending-end converter transformer, respectively. dr0B U drB These are the valve-side reference voltage and DC reference voltage of the receiving-end converter transformer, respectively; Q dd Q dr The reactive power consumed by the sending and receiving end converters are respectively; P dd P dr These represent the active power consumed by the sending and receiving end converters, respectively; I d U is the current at the DC end of the converter station. td U tr These are the converter bus node voltages at the sending and receiving ends, respectively; k Td k Tr These are the transformer turns ratios of the sending and receiving end converter stations, respectively; X d X r These are the equivalent reactances of the converter transformers at the sending and receiving ends of the converter stations, respectively; R d U is the equivalent resistance of a DC transmission line. dd0 U dd These are the valve-side voltage and DC voltage of the sending-end converter transformer, respectively; U dr0 U dr These are the valve-side voltage and DC voltage of the receiving-end converter transformer, respectively. 2) When the DC system does not inject power into the AC system, establish the steady-state power flow equations for the pure AC system, i.e.: In the formula, ΔP and ΔQ are the imbalance matrices of active and reactive power of the AC bus, respectively; Δδ and ΔU are the correction matrices of phase angle and amplitude of AC bus voltage, respectively; J Pδ J PU J Qδ J QU These are the four corresponding submatrices of the Jacobian matrix J; 3) When a DC system supplies power to an AC system, the submatrix J in the Jacobian matrix J... PU J QU The diagonal elements are corrected, and the corrected element J PU '、Element J QU As shown in the following formula: Where, when node i is the sending-end converter bus node, s i =1; when node i is the receiving-end converter bus node, s i =-1; U i P is the voltage at node i; dci Q dci Let i be the active power and reactive power of DC node i. 4) Establish the control equations for the sender and receiver converter station controllers, namely: In the formula, P dd The active power consumed by the sending-end converter; γ is the inverter station turn-off angle; P dd sp γ sp The planned values ​​for the active power consumed by the sending-end converter and the inverter station turn-off angle; 5) Establish the external characteristic equations for the rectifier station and inverter station connected to the AC system, namely: The partial derivatives of the active power transmitted and reactive power consumed by the two converter stations with respect to the voltage amplitude of the converter bus are as follows: In the formula, D d D r To calculate the relevant parameters of the DC state variables at the sending and receiving ends; The partial derivative of reactive power consumed by the sending-end converter station with respect to the voltage of the receiving-end converter bus; Among them, the partial derivative of the DC current with respect to the amplitude of the receiving-end converter bus voltage. As shown below:

3. The AC / DC system coordinated two-stage voltage control method considering DC control mode according to claim 1, characterized in that, The objective function of the AC / DC coordinated two-stage voltage control model M, which considers the correlation between DC transmitters and receivers, is shown below: In the formula, W c W t and W q As the weight, and W c >W q W t >W q ; and These are the initial value and ideal reference value of the voltage vector at the central node, respectively, both with dimension n. c ×1; and These are the initial value and the set reference value of the voltage vector at the receiving-end converter bus node, respectively, both with dimension n. dr ×1;n c n g and n dr These represent the number of AC central nodes, controlled power plant nodes, and converter station nodes at the receiving end of the power grid, respectively; C c C t These are the sensitivity matrices of the central node and converter bus node voltages to the generator terminal voltage, respectively, with dimensions n. c ×n g n dr ×n g μ g and ΔU g These are the generator reactive power balancing factor and the generator terminal voltage regulation vector, respectively, both with dimension n. g ×1, where the i-th component is μ gi ; These are the initial value, lower limit, and upper limit vectors of the generator reactive power output, each with dimension n. g ×1; These are the elements of the generator reactive power output initial value, lower limit, and upper limit vector, respectively; C g Let n be the sensitivity matrix of the generator reactive power output to the generator terminal voltage. g ×n g C gi C g The i-th row.

4. The AC / DC system coordinated two-stage voltage control method considering DC control mode according to claim 1, characterized in that, The constraints of the AC / DC coordinated two-level voltage control model M, which considers the correlation between the DC sending and receiving ends, include the power flow constraints of the AC system, the power flow constraints of the converter nodes, the network security constraints of the AC / DC system, the characteristic equation constraints of the sending and receiving end converters, the dead zone constraints of the AC filter / parallel capacitor switching of the reactive power at the converter gate, the control variable constraints of the sending end converter station, and the control variable constraints of the receiving end converter station. The characteristic equations of the sending and receiving end converters are constrained as shown in equation (1), that is: In the formula, α is the trigger angle, γ is the turn-off angle; N d N r The number of six-pulse converters per pole at the sending and receiving ends, respectively; k pd k pr These represent the number of operating poles of the sending and receiving end converters, respectively; T d =U dd0B / U ddB T r =U dr0B / U drB These are the conversion coefficients for the sending and receiving end reference values, respectively; U dd0B U ddB These are the valve-side reference voltage and DC reference voltage of the sending-end converter transformer, respectively. dr0B U drB These are the valve-side reference voltage and DC reference voltage of the receiving-end converter transformer, respectively; Q dd Q dr The reactive power consumed by the sending and receiving end converters are respectively; P dd P dr These represent the active power consumed by the sending and receiving end converters, respectively; I d U is the current at the DC end of the converter station. td U tr These are the converter bus node voltages at the sending and receiving ends, respectively; k Td k Tr These are the transformer turns ratios of the sending and receiving end converter stations, respectively; X d X r These are the equivalent reactances of the converter transformers at the sending and receiving ends of the converter stations, respectively; R d U is the equivalent resistance of a DC transmission line. dd0 U dd These are the valve-side voltage and DC voltage of the sending-end converter transformer, respectively; U dr0 U dr These are the valve-side voltage and DC voltage of the receiving-end converter transformer, respectively.

5. The AC / DC system coordinated two-stage voltage control method considering DC control mode according to claim 1, characterized in that, The power flow constraints of the communication system are as follows: In the formula, P Gi Q Gi P represents the active and reactive power generated by the power source at AC node i, respectively; Li Q Li U represents the active and reactive power absorbed by the load at AC node i, respectively; i G represents the voltage at node i. ij B ij δ ij U represents the conductance, susceptance, and phase angle difference of line ij, respectively; j This represents the voltage at node j; The power flow constraints of the converter node are as follows: In the formula, U d I is the voltage to ground at the DC terminal of the converter station. d d represents the current at the DC end of the converter station. ij The phase angle difference of the branch where the converter station is located; The power factor angle of the converter; The network security constraints for AC / DC systems are as follows: D.U. h =C h D.U. g (12) In the formula, ΔU h and The adjustment amount and maximum allowable value of the high-voltage bus voltage of the power plant are given, with dimension n. g ×1;C h This is the sensitivity matrix of the high-voltage bus voltage of the power plant to the generator terminal voltage, with dimension n. g ×n g ; and These represent the initial value, lower limit, and upper limit of the high-voltage bus voltage at the power plant, respectively, each with dimension n. g ×1; and These represent the initial value, lower limit, and upper limit of the central node voltage, respectively, each with dimension n. c ×1; and These represent the initial value, lower limit, and upper limit of the receiving-end converter bus node voltage, respectively, each with dimension n. dr ×1; and Let n represent the initial value, lower limit, and upper limit of the generator terminal voltage, respectively, each with dimension n. g ×1;C g This is the sensitivity matrix of the generator reactive power output to the generator terminal voltage; These are the initial value, lower limit, and upper limit vectors of the generator's reactive power output, respectively; C c C t These are the sensitivity matrices of the central node and converter bus node voltages to the generator terminal voltage, respectively; ΔU g C is the generator terminal voltage regulation vector; g This is the sensitivity matrix of the generator reactive power output to the generator terminal voltage; The dead-time constraints for switching AC filters / parallel capacitors at the converter gate reactive power are shown below: In the formula, C nd C nr These are the sensitivity matrices of reactive power at the converter station gates of the sending and receiving ends to the generator terminal voltage, respectively, with dimensions n. dd ×n g n dr ×n g ; These are the initial values ​​for reactive power exchanged at the converter gates at the sending and receiving ends, respectively, both with dimension n. dr ×1;Q dzd Q dzr The control dead zones of the AC filters / parallel capacitors at the converter gates of the sending and receiving ends are respectively, with dimensions n. dd ×1、n dr ×1; Let n be the initial values ​​of the reactive power compensation at the sending and receiving ends, respectively, with dimensions n. dd ×1、n dr ×1; Let n be the initial values ​​of the reactive power consumed by the sending and receiving end converters, respectively, with dimensions n. dd ×1、n dr ×1;n dd n dr These represent the number of converter station nodes in the DC near-area power grid at both the sending and receiving ends; The control variable constraints for the sending-end converter station are as follows: In the formula, and Let n be the initial value, lower limit, and upper limit of the cosine of the firing angle of the sending-end converter, each with dimension n. dd ×1;C dd Let n be the sensitivity matrix of the converter firing angle cosine to the generator terminal voltage, with dimension n. dd ×n g ; The control variable constraints for the receiving-end converter station are as follows: In the formula, and Let n be the initial value, lower limit, and upper limit of the no-load voltage on the valve side of the receiving-end converter transformer, each with dimension n. dr ×1;C dr Let n be the sensitivity matrix of the unloaded voltage on the valve side of the receiving-end converter transformer to the generator terminal voltage. dr ×n g .

6. The AC / DC system coordinated two-stage voltage control method considering DC control mode according to claim 1, characterized in that, Tools for solving the AC / DC coordinated two-stage voltage control model M that considers the DC-DC transmission-receiver correlation include CPLEX.

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