Direct current control mode pre-judgment method for alternating current and direct current power flow calculation

Abstract

The invention discloses a direct current control mode pre-judgment method for alternating current and direct current power flow calculation, which comprises the following steps of: modeling a direct current system, listing and writing a circuit characteristic equation of the alternating current and direct current system, and then writing a control characteristic equation according to a direct current operation characteristic curve to obtain a mathematical relationship between a current conversion bus voltage and a direct current voltage; then, direct-current control mode boundary conditions are introduced, the mathematical relationship between the direct-current control mode and the commutation bus voltage and the mathematical relationship between the direct-current control mode and the power supply voltage are established, and alternating-current and direct-current system line parameters and an alternating-current power supply are input, so that pre-judgment of the control mode of the direct-current system can be completed; the expansion effect of alternating current control actions (such as transformer tap adjustment) on the direct current operation interval is evaluated, an alternating current side control instruction is corrected, the direct current control mode of the direct current system is judged, meanwhile, it is ensured that the direct current system always operates in the target operation interval, and alternating current and direct current load flow calculation convergence is improved.

Description

Technical Field

[0001] This invention relates to the field of power systems and their automation technology, specifically to a method for predicting DC control modes for AC / DC power flow calculation. Background Technology

[0002] Power flow analysis, as a core functional module of modern energy management systems (EMS), has become a research hotspot in the industry, particularly in AC / DC hybrid power grids containing high-voltage direct current (HVDC) transmission. However, existing alternating iterative methods still face technical bottlenecks at the control coordination level.

[0003] When the system operates under special conditions such as voltage / power reduction, the rapid adjustment characteristics of the DC system and the slow-speed control equipment on the AC side (such as on-load tap-changing transformers) are difficult to coordinate effectively. In weak AC grid scenarios, this can easily lead to oscillations and instability in voltage-reactive power parameters. Currently, convergence adjustments are mainly made based on manual experience, which can easily cause calculation results to oscillate or diverge, resulting in low efficiency and insufficient reliability. Traditional calculation methods use fixed DC parameter assumptions, which not only do not conform to actual control logic but also easily lead to inaccurate calculation results.

[0004] The innovative method proposed in this invention establishes a DC control mode identification mechanism to determine the converter station control mode and key parameters during power flow calculation. By dynamically correcting the AC control parameters, the DC system is guided to the target operating range, which effectively improves the convergence under uncertain operating modes and significantly enhances the engineering applicability of the calculation results. Summary of the Invention

[0005] In view of this, the present invention provides a method for predicting DC control modes for AC / DC power flow calculation. By establishing a DC control mode identification mechanism, the control mode and key parameters of the converter station are dynamically determined and adjusted during the power flow calculation process, which effectively improves the convergence under uncertain operating modes and significantly enhances the engineering applicability of the calculation results.

[0006] A method for predicting DC control modes for AC / DC power flow calculation, applied to power flow analysis of AC / DC systems, the method comprising:

[0007] First, model the DC system and write out the circuit characteristic equations of the AC / DC system. Then, write out the control characteristic equations based on the DC operating characteristic curves.

[0008] Based on the circuit characteristic equations and control characteristic equations of the AC / DC system, the mathematical relationship between the converter bus voltage and the DC voltage is obtained. Then, the boundary conditions of the DC control mode are introduced to establish the mathematical mapping relationship between the DC control mode and the converter bus voltage.

[0009] Based on the circuit characteristic equations and control characteristic equations of the AC / DC system, the mathematical relationship between the converter bus voltage and the power supply voltage is obtained. Based on this, the mathematical mapping relationship between the DC control mode and the converter bus voltage is transformed into the mathematical mapping relationship between the DC control mode and the power supply voltage and DC power. This allows for the prediction of the control mode of the DC system based on the operating characteristic quantities of the AC system.

[0010] Then, based on the DC operating characteristic curve, the target operating range of DC is given, and the expansion effect of AC control actions (such as transformer tap adjustment) on the DC operating range is evaluated. The AC / DC system line parameters and AC power supply are input, the AC side control commands are corrected, and the DC control mode of the DC system is determined while ensuring that the DC system always operates within the target operating range.

[0011] Furthermore, the AC / DC system is modeled, the circuit characteristic equations of the AC / DC system are written, and then the control characteristic equations are determined based on the DC operating characteristic curve. Specifically, this includes:

[0012] The characteristic equations of AC / DC system circuits include the characteristic equations of DC system circuits and the power equations of AC / DC systems. The circuit characteristic equations are shown below:

[0013]

[0014] Where θ is the trigger angle (extinguishing angle); The power factor angle; K b Indicates the number of converter bridges; X T U is the converter reactance. T is the converter transformer turns ratio; U d This is the DC side voltage; I d R is the direct current; d E0 is the DC resistance; E0 is the power supply voltage; U ac θ is the converter bus voltage; Uac θ represents the phase angle of the converter bus voltage. E0 Represents the phase angle of the power supply voltage; θ z Z represents the AC impedance angle; B represents the AC impedance. c P represents ground susceptance; d For DC power transmission; Q d For DC reactive power transmission; P ac For alternating active power; P c Q represents the active power of the converter bus to ground. ac For AC reactive power; Q c This refers to the reactive power of the converter bus to ground.

[0015] The AC / DC power equations on the rectifier side are as follows:

[0016]

[0017] The AC / DC power equations for the inverter side are similar.

[0018] Wherein, the subscript r represents the rectifier side; the subscript i represents the inverter side;

[0019] Based on the DC operating characteristic curve, the control characteristic equation for the rectifier side is:

[0020]

[0021] The inverter-side control characteristic equation is:

[0022]

[0023] Where the subscript r represents the rectifier side; the subscript i represents the inverter side; I B U is the rated DC current. d For DC voltage, I dH I dmin I represents the upper and lower limits of the VDCOL DC current. dmin Also for a fixed minimum current, A vd B vd K is the VDCOL control coefficient. c θ is the current deviation coefficient. min This is the minimum firing angle (extinguishing angle).

[0024] Furthermore, based on the AC / DC system circuit characteristic equations and control characteristic equations, the converter bus voltage U is obtained. ac With DC voltage U d The mathematical relationship between the DC control mode and the converter bus voltage U is established by introducing the boundary conditions of the DC control mode. ac The mathematical mapping relationship is represented by line segments in the DC operating characteristic curve, such as ACEG and AHIJ.

[0025] Converter bus voltage U ac With DC voltage U d The mathematical relationship is as follows:

[0026]

[0027] Among them, F d(X) DC voltage U d Relevant quantity, L (A) These are the relevant quantities for the converter transformer turns ratio T. The subscript (A) represents point A on the operating characteristic curve; the subscript (X) represents any point on the operating characteristic curve.

[0028] The boundary conditions for DC control are as follows:

[0029]

[0030] DC control method and converter bus voltage U ac The mathematical mapping relationship is as follows:

[0031]

[0032] In this context, the subscripts (H), (I), and (A) represent points H, I, and A on the operating characteristic curve, respectively.

[0033] Furthermore, by combining the circuit characteristic equations and control characteristic equations of the AC / DC system, the converter bus voltage U is obtained. ac The mathematical relationship between the power supply voltage E0 and the DC control method and the converter bus voltage U is established, and based on this, the DC control method is compared with the converter bus voltage U. ac The mathematical mapping relationship is transformed into the DC control mode and the power supply voltage E0 and DC power P. d The mathematical mapping relationship.

[0034] Converter bus voltage U ac The mathematical relationship between the voltage E0 and the power supply voltage is as follows:

[0035]

[0036] Squaring both sides of the above equation and adding them together eliminates θ. Uac It can be deduced that:

[0037]

[0038] It can be written as: E 0(X) =f E0(X) (U ac(X) )

[0039] Similarly: P d(X) =f Pd(X) (U ac(X) )

[0040] The predicted impact of power supply voltage E0 on the control method of the DC system is as follows:

[0041]

[0042] Furthermore, based on the DC operating characteristic curve, the target DC operating range is given, generally the AC segment. The target DC operating range is written as:

[0043]

[0044] Then, based on the evaluation of the expansion effect of AC control actions (such as transformer tap adjustment) on the DC operating range according to the target DC operating range, the AC side control commands are corrected, and the DC control mode of the DC system is determined. Simultaneously, it is ensured that the DC system always operates within the target operating range, improving the computational convergence under uncertain operating conditions. The judgment is as follows:

[0045] Input AC / DC system line parameters and AC power supply, and generate feedback quantity U′ during power flow calculation. ac When the feedback quantity satisfies the following formula:

[0046] l r(A) U′ acr <l i(A) U′ aci +M (A)

[0047] Modify the AC side control commands to improve l r(A) , reduce l i(A) This ensures that the target operating range conditions are met.

[0048] When the feedback quantity satisfies the following formula: U acr <U aci(C) =F di(C) / l i(A)

[0049] Modify the AC side control commands to improve l i(A) This will ensure that the conditions for the target operating range are met. If not, repeat the above steps until the DC system consistently operates within the target operating range.

[0050] The present invention has the following advantages over the prior art:

[0051] This invention proposes a method for predicting DC control modes in AC / DC power flow calculations. By establishing a DC control mode identification mechanism, the control mode and key parameters of the converter station are dynamically determined and adjusted during the power flow calculation process, ensuring that the DC system always operates within the target operating range. This effectively improves the convergence under uncertain operating modes and significantly enhances the engineering applicability of the calculation results. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0053] Figure 1The flowchart for predicting the DC control mode in Embodiment 1 of the present invention is shown in the abstract figure.

[0054] Figure 2 This is a flowchart illustrating the determination of the DC control mode in Embodiment 1 of the present invention.

[0055] Figure 3 This is a comparison diagram of power flow calculation in Embodiment 1 of the present invention.

[0056] Figure 4 This is a schematic diagram of the equivalent model of the AC / DC system in Embodiment 1 of the present invention.

[0057] Figure 5 This is a curve showing the operating characteristics of a DC system according to Embodiment 1 of the present invention.

[0058] Figure 6 This is a segmented interval equivalent diagram of the DC system operating characteristic curve of Embodiment 1 of the present invention.

[0059] Figure 7 This is a schematic diagram of the DC system control mode adjustment in Embodiment 1 of the present invention. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] Example 1:

[0062] like Figure 1 As shown in the figure, this embodiment provides a method for predicting DC control mode in AC / DC power flow calculation. The specific flowchart for determining the DC control mode is as follows. Figure 2 As shown, when applied to power flow calculation, the convergence is compared to... Figure 3 As shown, this method is applied to high-voltage direct current transmission systems and includes the following steps:

[0063] S1, such as Figure 4 As shown, the AC / DC system is modeled, and the circuit characteristic equations of the AC / DC system are written, such as... Figure 5 As shown, the control characteristic equations are then derived based on the DC operating characteristic curves. The AC / DC system circuit characteristic equations include the DC system circuit characteristic equations and the AC / DC system power equations. The circuit characteristic equations are shown below:

[0064]

[0065] The AC / DC power equations on the rectifier side are as follows:

[0066]

[0067] The AC / DC power equations for the inverter side are similar, and the control characteristic equations for the rectifier side are derived from the DC operating characteristic curve.

[0068] S2. Based on the AC / DC system circuit characteristic equations and control characteristic equations, the converter bus voltage U is obtained. ac With DC voltage U d The mathematical relationship is then introduced, followed by the boundary conditions for DC control, such as... Figure 5 As shown, the DC control mode and the converter bus voltage U are established. ac The mathematical mapping relationship.

[0069] S21, Converter bus voltage U ac With DC voltage U d The mathematical relationship is as follows:

[0070]

[0071] Among them, F d(X) DC voltage U d Relevant quantities, l (A) These are the relevant quantities for the converter transformer turns ratio T. The subscript (A) represents point A on the operating characteristic curve; the subscript (X) represents any point on the operating characteristic curve.

[0072] S22. The boundary conditions for DC control mode are as follows:

[0073]

[0074] like Figure 6 As shown, the DC control mode and the converter bus voltage U ac The mathematical mapping relationship is as follows:

[0075]

[0076] In this context, the subscripts (H), (I), and (A) represent points H, I, and A on the operating characteristic curve, respectively.

[0077] S3. Combining the AC / DC system circuit characteristic equations and control characteristic equations, the converter bus voltage U is obtained. ac The mathematical relationship between the power supply voltage E0 and the DC control method and the converter bus voltage U is established, and based on this, the DC control method is compared with the converter bus voltage U. ac The mathematical mapping relationship is transformed into the DC control mode and the power supply voltage E0 and DC power P. d The mathematical mapping relationship.

[0078] S31. Combining the aforementioned AC / DC system circuit characteristic equations and control characteristic equations, the converter bus voltage U... ac The mathematical relationship between the voltage E0 and the power supply voltage is as follows:

[0079]

[0080] Squaring both sides of the above equation and adding them together eliminates θ. Uac It can be deduced that:

[0081]

[0082] It can be written as: E 0(X) =f E0(X) (U ac(X) )

[0083] Similarly: P d(X) =f Pd(X) (U ac(X) )

[0084] S32, Connect the DC control mode with the converter bus voltage U ac The mathematical mapping relationship is transformed into the DC control mode and the power supply voltage E0 and DC power P. d Mathematical mapping relationships, such as Figure 2 As shown, the prediction of the control mode of the DC system based on the power supply voltage E0 is completed, as shown in the following formula:

[0085]

[0086] S4. Based on the DC operating characteristic curve, give the target DC operating range. For example... Figure 7 As shown, the AC control actions (such as transformer tap adjustment) are evaluated based on the DC target operating range to expand the DC operating range. The AC side control commands are adjusted, and the DC control mode of the DC system is determined while ensuring that the DC system always operates within the target operating range.

[0087] S41. Based on the DC operating characteristic curve, the target operating range for DC is given, which is generally the AC segment, as shown in the following formula:

[0088]

[0089] S42. Next, based on the DC target operating range, evaluate the expansion effect of AC control actions (such as transformer tap adjustment) on the DC operating range, adjust the AC side control commands, determine the DC control mode of the DC system, and ensure that the DC system always operates within the target operating range, improving the computational convergence under uncertain operating conditions. The judgment is as follows:

[0090] Input AC / DC system line parameters and AC power supply, and generate feedback quantity U′ during power flow calculation. ac When the feedback quantity satisfies the following formula:

[0091] l r(A) U′ acr <l i(A) U′ aci +M (A)

[0092] Adjust the AC side control commands to improve l r(A) , reduce l i(A) This ensures that the target operating range conditions are met.

[0093] When the feedback quantity satisfies the following formula:

[0094] U acr <U aci(C) =F di(C) / l i(A)

[0095] Adjust the AC side control commands to improve l i(A) This will ensure that the conditions for the target operating range are met. If not, repeat the above steps until the DC system consistently operates within the target operating range.

[0096] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware, and the corresponding program can be stored in a computer-readable storage medium.

[0097] It should be noted that although the method operations of the above embodiments are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. On the contrary, the order of execution of the described steps may be changed. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

Claims

1. A method for predicting DC control modes for AC / DC power flow calculation, applied to power flow analysis of AC / DC systems, the method comprising: First, model the DC system and write out the circuit characteristic equations of the AC / DC system. Then, write out the control characteristic equations based on the DC operating characteristic curves. Based on the circuit characteristic equations and control characteristic equations of the AC / DC system, the mathematical relationship between the converter bus voltage and the DC voltage is obtained. Then, the boundary conditions of the DC control mode are introduced to establish the mathematical mapping relationship between the DC control mode and the converter bus voltage. Based on the circuit characteristic equations and control characteristic equations of the AC / DC system, the mathematical relationship between the converter bus voltage and the power supply voltage is obtained. Based on this, the mathematical mapping relationship between the DC control mode and the converter bus voltage is transformed into the mathematical mapping relationship between the DC control mode and the power supply voltage and DC power, thus completing the prediction of the control mode of the DC system by the AC system operating characteristic quantities. Then, based on the DC operating characteristic curve, the target operating range of the DC system is given, and the expansion effect of AC control actions (such as transformer tap adjustment) on the DC operating range is evaluated. The AC side control commands are adjusted, and the DC operating status of the DC system is determined while ensuring that the DC system always operates within the target operating range.

2. The DC control mode prediction method for AC / DC power flow calculation according to claim 1, characterized in that, Based on the AC / DC system circuit characteristic equations and control characteristic equations, the converter bus voltage U is obtained. ac With DC voltage U d The mathematical relationship between the DC control mode and the converter bus voltage U is established by introducing the boundary conditions of the DC control mode. ac The mathematical mapping relationship is represented by line segments in the DC operating characteristic curve, such as ACEG and AHIJ. Converter bus voltage U ac With DC voltage U d The mathematical relationship is as follows: And ac(X) =F d(X) / l (A) l (A) =T cosθ min Among them, F d(X) DC voltage U d Relevant quantities, l (A) These are the relevant quantities for the converter transformer turns ratio T. The subscript (A) represents point A on the operating characteristic curve; the subscript (X) represents any point on the operating characteristic curve. The boundary conditions for DC control are as follows: l r(A) U acr =l i(A) U aci +M (A) ACEG:l r(A) YOU acr >l i(A) YOU aci +M (A) AHIJ:l r(A) U acr <l i(A) U aci +M (A) DC control method and converter bus voltage U ac The mathematical mapping relationship is as follows: l r(A) U acr =l i(A) U aci +M (A) A In this context, the subscripts (H), (I), and (A) represent points H, I, and A on the operating characteristic curve, respectively.

3. The method for predicting DC control mode in AC / DC power flow calculation according to claim 1, characterized in that, The converter bus voltage U is obtained by combining the AC / DC system circuit characteristic equations and control characteristic equations. ac The mathematical relationship with the power supply voltage E0. Specifically, this includes: Converter bus voltage U ac The mathematical relationship between the voltage E0 and the power supply voltage is as follows: Squaring both sides of the above equation and adding them together eliminates θ. Uac It can be deduced that: E 0(X) 2 =(a c(X) U ac(X) 2 +b c(X) U ac(X) +c c(X) ) 2 / U ac(X) 2 +(a s(X) U ac(X) 2 +b s(X) U ac(X) +c s(X) ) 2 / U ac(X) 2 It can be written as: HAVE BEEN 0(X) =f E0(X) (U ac(X) ) Similarly: P d(X) =f Pd(X) (U ac(X) ) 4. The method for predicting DC control mode in AC / DC power flow calculation according to claim 1, characterized in that... Based on the converter bus voltage U ac The mathematical relationship between the power supply voltage E0 and the DC control mode and the converter bus voltage U ac The mathematical mapping relationship is transformed into the DC control mode and the power supply voltage E0 and DC power P. d The mathematical mapping relationships specifically include: The predicted impact of power supply voltage E0 on the control method of the DC system is as follows:

5. The method for predicting DC control mode in AC / DC power flow calculation according to claim 1. Its characteristic is that... The target operating range for DC is given based on the DC operating characteristic curve, specifically including: Based on the DC operating characteristic curve, the target operating range for DC is given. The target operating range for DC is the AC segment, written as:

6. The method for predicting DC control mode in AC / DC power flow calculation according to claim 1. Its characteristic is that... Evaluate the expansion effect of AC control actions (such as transformer tap adjustment) on the DC operating range, correct AC side control commands, determine the DC operating status of the DC system, and ensure that the DC system always operates within the target operating range. Specifically, this includes: Given an initial voltage U ac Feedback quantity U′ is generated during power flow calculation. ac If the feedback quantity satisfies the following formula: l r(A) U′ acr <l i(A) U′ aci +M (A) Adjust the AC side control commands to improve l r(A) , reduce l i(A) This ensures that the target operating range conditions are met. When the feedback quantity satisfies the following formula: And acr <And aci(C) =F di(C) / l i(A) Adjust the AC side control commands to improve l i(A) This will ensure that the conditions for the target operating range are met. If not, repeat the above steps until the DC system consistently operates within the target operating range.

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