Improved power flow algorithm of multi-terminal direct current partition interconnected power grid

Abstract

The invention discloses an improved power flow algorithm for a multi-terminal direct-current partition interconnected power grid, which comprises the following steps of: inputting state information of PCC nodes of a power station into an alternating-current power grid connected with the power station, and carrying out alternating-current power flow calculation; carrying out power station load flow calculation according to an alternating current load flow calculation result; according to the load flow calculation result of the power station, carrying out rapid linear load flow calculation on the DC power grid; carrying out voltage station load flow calculation according to a direct current load flow calculation result; and inputting the state information of the PCC node of the voltage station into an alternating current power grid connected with the voltage station, and carrying out alternating current load flow calculation. Compared with a traditional alternating current and direct current power flow algorithm and an existing improved algorithm, on the premise that the power flow calculation accuracy is guaranteed, the universal flexibility of the algorithm is improved, the calculation burden is reduced, cyclic calculation is not needed, the number of iterations of power flow calculation is greatly reduced, and the calculation efficiency is improved; the method can be widely applied to load flow calculation work of a multi-terminal direct-current partition interconnected power grid.

Description

Technical Field

[0001] The invention belongs to the technical field of power flow calculation of multi-terminal DC partitioned interconnected power grids, and in particular relates to an improved power flow algorithm for multi-terminal DC partitioned interconnected power grids. Background Art

[0002] As the global energy structure accelerates its low-carbon transformation, the penetration rate of renewable energy represented by wind power and photovoltaics continues to rise. Driven by my country's "dual carbon" strategic goal, the new power system presents the significant characteristics of high proportion of renewable energy access and multi-level DC interconnection. However, the inherent volatility and geographical dispersion of renewable energy output pose severe challenges to the voltage regulation and power balance of traditional AC power grids. In this context, the flexible DC transmission technology based on voltage source converter (VSC) has become a key enabling equipment for building multi-terminal DC zone interconnected power grids with its technical advantages such as flexible controllability and no commutation failure risk. Typical projects include the Zhangbei ±500kV flexible DC grid demonstration project, the Nan'ao three-terminal flexible DC demonstration project, and the Zhejiang Zhoushan five-terminal flexible DC demonstration project. The multi-terminal DC system forms a modular structure with power mutual assistance and fault isolation through zone interconnection, but the coupling effect of its network topology complexity and VSC's diversified control mode brings new theoretical difficulties to the accurate calculation of system power flow distribution.

[0003] As a basic tool for steady-state analysis of power grids, the accuracy and efficiency of power flow calculation directly determine the rationality of the system operation mode and the reliability of safety margin assessment. The power flow algorithm of traditional AC power grids is already mature. The power flow algorithms for DC partitioned interconnected power grids mainly include unified iteration method and alternating iteration method. The unified iteration method has good convergence, but it needs to calculate the Jacobian matrix of the entire interconnected power grid, which leads to a high computational burden. In addition, the unified iteration method requires a large modification of the AC Jacobian matrix, so it has poor inheritance to the existing AC power flow algorithm. The alternating iteration method realizes the separate calculation of AC and DC power grids, with a lighter computational burden, and has good adaptability to the existing AC power flow algorithm, and can flexibly modify the AC and DC system structure. Therefore, the alternating iteration method has attracted more attention. However, the alternating iteration method requires cyclic calculation of the power flow of the AC power grid, DC power grid, and converter station, and each power flow calculation requires iteration, so the computational efficiency is low.

[0004] Faster calculation speed, better general flexibility, reliable convergence and lower computational burden have always been pursued by inventors in the field of power flow calculation. Therefore, how to further improve the efficiency of the algorithm while maintaining the good general flexibility and low computational burden of the alternating iteration method has become a research focus in this field. However, the existing improved power flow algorithms for multi-terminal DC partitioned interconnected power grids often improve the computational efficiency by 1) redividing the boundaries of the AC and DC power grids, 2) introducing new variables, 3) ignoring the detailed converter active loss model, 4) redefining the VSC control method, 5) providing good iterative initial values, 6) modifying the converter model, and 7) adding power flow correction links. Although these algorithms improve the computational efficiency, they always require major changes to the original algorithms, and many improved algorithms still require AC power flow and DC power flow cyclic calculations.

[0005] In fact, the key to improving the efficiency of the AC / DC power flow algorithm is to decouple the alternating iteration method so that the AC power grid, DC power grid, and converter station power flow can be calculated separately without loop calculation. Moreover, if we can achieve a more "natural" decoupling effect without making major changes to the AC / DC power grid and the algorithm on the basis of decoupling, this will further improve the general flexibility of the algorithm. Summary of the invention

[0006] The present invention is proposed to solve the problems of poor general flexibility and slow solution speed of the current solution algorithm of multi-terminal DC partition interconnected power grid in the prior art, and its purpose is to provide an improved current algorithm of multi-terminal DC partition interconnected power grid.

[0007] The technical solution of the present invention is: an improved power flow algorithm for a multi-terminal DC partition interconnected power grid, comprising the following steps:

[0008] A. Input the status information of the PCC node of the power station into the AC power grid connected to the power station to perform AC power flow calculation;

[0009] B. Perform power station power flow calculation based on the AC power flow calculation results;

[0010] C. Perform fast linear power flow calculation on the DC grid based on the power station power flow calculation results;

[0011] D. Perform voltage station power flow calculation based on DC power flow calculation results;

[0012] E. Input the status information of the PCC node of the voltage station into the AC power grid connected to the voltage station to perform AC power flow calculation.

[0013] Furthermore, step A inputs the status information of the PCC node of the power station into the AC power grid connected to the power station to perform AC power flow calculation. The specific process is as follows:

[0014] First, the AC power flow calculation lacks the PCC node status information of the VSC converter station, while the PCC node status information of the power station is complete;

[0015] Then, for the multi-terminal DC zoned interconnected power grid, the power flow calculation is first performed on the AC power grid connected to the power station;

[0016] Finally, the AC power flow calculation model is established and the AC power flow calculation is performed.

[0017] Furthermore, the PCC node status information consists of active power and reactive power, or consists of active power and voltage amplitude.

[0018] Furthermore, step B performs power station power flow calculation based on the AC power flow calculation result. The specific process is as follows:

[0019] First, after the AC power flow calculation, the voltage amplitude and phase angle, or reactive power and voltage phase angle, of the PCC node of the power station are obtained;

[0020] Then, the power station power flow calculation is performed by combining the AC power flow calculation results with the known status information of the power station PCC node;

[0021] Finally, the active power injected into the DC grid by the power station is obtained.

[0022] Furthermore, step C performs fast linear power flow calculation on the DC grid according to the power station power flow calculation result. The specific process is as follows:

[0023] Firstly, a fast linear power flow model of the DC grid is established;

[0024] Then, after obtaining the active power injected into the DC grid by the power station, the fast linear power flow model is used to calculate the fast linear power flow of the DC grid;

[0025] Finally, the DC power grid flow calculation results are obtained.

[0026] Furthermore, step D performs voltage station power flow calculation based on the DC power flow calculation result. The specific process is as follows:

[0027] First, after the power flow of the DC grid is solved, the active power injected into the DC grid by the voltage station is obtained;

[0028] Then, the active power injected into the AC grid by the voltage station is obtained through the voltage station power flow model;

[0029] Finally, the voltage station power flow model is established and the voltage station power flow calculation is performed.

[0030] Furthermore, step E inputs the status information of the voltage station PCC node into the AC power grid connected to the voltage station to perform AC power flow calculation. The specific process is as follows:

[0031] First, after the voltage station power flow is solved, the status information of the PCC node of the voltage station is obtained;

[0032] Then, the power flow calculation is performed on the AC power grid connected to the voltage station.

[0033] Furthermore, the AC power flow calculation model in step A and step E is the same.

[0034] The beneficial effects of the present invention are as follows:

[0035] The present invention achieves a relatively "natural" decoupling of AC and DC power flows without changing the interconnected power grid and converter station structure, taking into account different control modes and detailed loss models of VSC, adding no correction links, and introducing no new variables.

[0036] Compared with traditional AC / DC power flow algorithms and existing improved algorithms, the present invention improves the general flexibility of the algorithm and reduces the calculation burden while ensuring the accuracy of power flow calculation. It also does not require cyclic calculations, greatly reduces the number of iterations of power flow calculations, and improves calculation efficiency. The present invention can be widely used in power flow calculations of multi-terminal DC partitioned interconnected power grids. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the method of the present invention;

[0038] Figure 2 It is a schematic diagram of the structure of the VSC converter station in the present invention;

[0039] Figure 3 It is a multi-terminal DC zoned interconnected power grid topology diagram adopted in the specific implementation mode of the present invention. DETAILED DESCRIPTION

[0040] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and embodiments:

[0041] like Figures 1 to 3 As shown, an improved power flow algorithm for a multi-terminal DC partitioned interconnected power grid includes the following steps:

[0042] A. Input the status information of the PCC node of the power station into the AC power grid connected to the power station to perform AC power flow calculation;

[0043] B. Perform power station power flow calculation based on the AC power flow calculation results;

[0044] C. Perform fast linear power flow calculation on the DC grid based on the power station power flow calculation results;

[0045] D. Perform voltage station power flow calculation based on DC power flow calculation results;

[0046] E. Input the status information of the PCC node of the voltage station into the AC power grid connected to the voltage station to perform AC power flow calculation.

[0047] Step A inputs the status information of the PCC node of the power station into the AC power grid connected to the power station to perform AC power flow calculation. The specific process is as follows:

[0048] First, the AC power flow calculation lacks the PCC node status information of the VSC converter station, while the PCC node status information of the power station is complete;

[0049] Then, for the multi-terminal DC zoned interconnected power grid, the power flow calculation is first performed on the AC power grid connected to the power station;

[0050] Finally, the AC power flow calculation model is established and the AC power flow calculation is performed.

[0051] The PCC node status information consists of active power and reactive power, or active power and voltage amplitude.

[0052] Step B performs power station power flow calculation based on the AC power flow calculation results. The specific process is as follows:

[0053] First, after the AC power flow calculation, the voltage amplitude and phase angle, or reactive power and voltage phase angle, of the PCC node of the power station are obtained;

[0054] Then, the power station power flow calculation is performed by combining the AC power flow calculation results with the known status information of the power station PCC node;

[0055] Finally, the active power injected into the DC grid by the power station is obtained.

[0056] Step C performs fast linear power flow calculation on the DC grid according to the power station power flow calculation results. The specific process is as follows:

[0057] Firstly, a fast linear power flow model of the DC grid is established;

[0058] Then, after obtaining the active power injected into the DC grid by the power station, the fast linear power flow model is used to calculate the fast linear power flow of the DC grid;

[0059] Finally, the DC power grid flow calculation results are obtained.

[0060] Step D performs voltage station power flow calculation based on the DC power flow calculation results. The specific process is as follows:

[0061] First, after the power flow of the DC grid is solved, the active power injected into the DC grid by the voltage station is obtained;

[0062] Then, the active power injected into the AC grid by the voltage station is obtained through the voltage station power flow model;

[0063] Finally, the voltage station power flow model is established and the voltage station power flow calculation is performed.

[0064] Step E inputs the status information of the voltage station PCC node into the AC power grid connected to the voltage station to perform AC power flow calculation. The specific process is as follows:

[0065] First, after the voltage station power flow is solved, the status information of the PCC node of the voltage station is obtained;

[0066] Then, the power flow calculation is performed on the AC power grid connected to the voltage station.

[0067] The AC power flow calculation model in step A is the same as that in step E.

[0068] Specifically, the AC power flow calculation model in step A is as follows:

[0069]

[0070] Where j and i represent the node numbers of the AC power grid, j∈i represents all nodes connected to the AC power grid node i, P Gi represents the active output of the generator at node i, P Li represents the active load of node i, U i represents the voltage amplitude of node i, δ ij represents the phase angle difference between node i and node j, G ij represents the conductance of the branch between node i and node j, B ij represents the inductance of the branch between node i and node j, Q Gi represents the reactive power output of the generator at node i, Q Li represents the reactive load of node i.

[0071] Specifically, the structure and electrical quantity reference direction of the VSC converter station in step B are as follows: Figure 2 As shown in the figure, the power station flow model is as follows:

[0072]

[0073] Where, I represents the current flowing through the converter station, P s represents the active power of the PCC node of the converter station, Q s represents the reactive power of the PCC node of the converter station, U s represents the voltage of the PCC node, U cRepresents the voltage on the AC side of the converter station, Z t is the transformer impedance, Z c Indicates the impedance of the commutation reactor, P loss Represents the active power loss of the converter, P dc It represents the active power injected into the DC grid by the converter station, a represents the quadratic coefficient of the converter active loss, b represents the linear coefficient of the converter active loss, c represents the constant coefficient of the converter active loss, j represents the imaginary unit, * represents the conjugate, and real represents taking the real part.

[0074] It can be seen from the power station flow model that solving the power station flow is only a simple circuit calculation and can be calculated without iteration.

[0075] Specifically, step C performs fast linear power flow calculation on the DC grid according to the power station power flow calculation result, as follows:

[0076] First, the fast linear power flow model of the DC grid is as follows:

[0077]

[0078] Among them, β i represents the droop coefficient of the i-th node, y ij represents the branch admittance between the i-th node and the j-th node, ΔU dc,i represents the difference between the voltage of the ith node and the reference value, P dcref,i represents the power reference value of the i-th node, P gen,i represents the active output of the generator at the ith node, P load,i represents the active load of the ith node, n dc Indicates the total number of DC grid nodes.

[0079] Then, for the DC grid nodes connected to the voltage stations without droop control, β is infinite; for the power stations and the DC grid nodes not connected to the VSC, β is zero.

[0080] Then, for the DC grid node connected to the power station, P dcref is the active power value P injected into the DC grid calculated by step B dc ; For voltage stations without droop control and DC grid nodes not connected to VSC, P dcref is zero.

[0081] Finally, after obtaining the active power injected into the DC grid by the power station, the above model is used to perform fast linear power flow calculation of the DC grid to obtain the DC grid power flow calculation result.

[0082] More specifically, the fast linear power flow model is a linear equation that can be solved in one step without iteration, thus speeding up the solution of the algorithm.

[0083] Specifically, the voltage station power flow model in step D is as follows:

[0084]

[0085] Wherein, R represents the sum of the resistances of the transformer and converter reactor of the converter station.

[0086] More specifically, when solving the above equation, the PCC node voltage phase angle δ s Or the voltage phase angle δ on the AC side of the converter c One is set to 0°. Because the purpose of solving the voltage station power flow is to obtain the active power P injected into the AC grid by the voltage station s , setting the phase angle on one side to 0° is equivalent to setting a balance node, which does not affect P s The accurate solution of .

[0087] More specifically, solving the voltage station power flow is a nonlinear equation, which is more complex and time-consuming than solving the power station power flow.

[0088] Specifically, the present invention does not modify the AC power flow algorithm, and can conveniently use related tools such as MATPOWER, PandaPower, or more advanced algorithms to perform AC power flow calculations.

[0089] Embodiment 1

[0090] An improved power flow algorithm for a multi-terminal DC zone interconnected power grid includes the following steps:

[0091] A. Input the status information of the PCC node of the power station into the AC power grid connected to the power station to perform AC power flow calculation;

[0092] B. Perform power station power flow calculation based on the AC power flow calculation results;

[0093] C. Perform fast linear power flow calculation on the DC grid based on the power station power flow calculation results;

[0094] D. Perform voltage station power flow calculation based on DC power flow calculation results;

[0095] E. Input the status information of the PCC node of the voltage station into the AC power grid connected to the voltage station to perform AC power flow calculation.

[0096] The structure of the VSC converter station used in this example is as follows Figure 2 As shown in Figure 1, the VSC converter station consists of filter inductors, transformers, and reactors. Figure 3As shown. Figure 3 It can be seen that the interconnected power grid consists of a 7-node DC grid connected to 3 IEEE33-node AC grids. In addition, the convergence criteria for AC and DC power flows are that the voltage deviation is less than 1×10 -9 Since the AC power grid adopts the IEEE standard calculation example, the specific parameters are not described in detail.

[0097] The 7-bus DC system parameters used in this example are shown in the following table

[0098] 7-bus DC system parameters

[0099]

[0100]

[0101] The VSC converter station parameters used in this example are shown in the following table

[0102] Basic parameters of converter station

[0103]

[0104] Currently, the VSC control methods of interconnected power grids are mostly single-point voltage control and multi-point voltage droop control. The present invention will start from these two control methods and show the superiority of the present invention by comparing with the traditional alternating iteration.

[0105] When single-point voltage control is adopted, the control parameters of the converter station are shown in the following table: Converter station control parameters (single-point voltage control)

[0106]

[0107] As can be seen from the table above, when single-point voltage control is adopted, VSC1 is the voltage station, which controls the voltage U of the DC node to which it is connected. dc and the reactive power Q at the PCC point s VSC2 and VSC3 are power stations that control the active power P of the PCC points to which they are connected. s and reactive power Q s When performing AC power flow calculations, the PCC nodes connected to VSC1 to VSC3 are considered as PQ nodes.

[0108] For AC power flow, since the PCC node status information of the power station is complete (active power and reactive power), AC Grid1 and AC Grid2 can directly perform AC power flow calculation at this time, and only the active power of the PCC node of the voltage station is lacking for the power flow calculation of AC Grid3.

[0109] For DC power flow, since the DC voltage of the voltage station is known, only the power injected into the DC grid by the power station is missing for DC grid power flow calculation.

[0110] When multi-point voltage droop control is adopted, the converter station control parameters are shown in the following table Converter station control parameters (multi-point voltage droop control)

[0111]

[0112] As can be seen from the above table, when multi-point voltage droop control is adopted, VSC1 and VSC2 are voltage stations, which control the reactive power Q of the PCC nodes to which they are connected. s , and controls the DC node voltage U to which it is connected dc and active power P dc Satisfy the following relationship

[0113] β(U dc -U dcref )+P dc -P dcref =0

[0114] At this time, for the AC power flow, since the PCC node status information of the power station is complete (active power and reactive power), AC Grid3 can directly perform AC power flow calculation. It only lacks the active power of the PCC node of the voltage station to perform power flow calculation of AC Grid1 and AC Grid2.

[0115] For the DC power flow, since the droop coefficient of the voltage station, the DC power reference value, and the DC voltage reference value are known, only the power injected into the DC grid by the power station is lacking for the DC grid power flow calculation.

[0116] Finally, the error of the improved power flow algorithm provided by the present invention is shown in the following table:

[0117]

[0118] It can be seen from the above table that the errors finally obtained by the present invention are all less than 0.1%, which is extremely small, so the results of the power flow calculation are reliable.

[0119] It is worth noting that the power flow error of the DC power grid of the present invention comes from the fast linear power flow calculation adopted. Because the algorithm ignores the quadratic term of voltage deviation, the maximum DC voltage deviation is usually 10%, so the error of linear power flow calculation is within 1%, which is acceptable.

[0120] In the AC power flow error, there is no error in AC Grid2 and AC Grid3 with single-point voltage control and AC Grid3 with multi-point voltage droop control, because the state information of the power station transmitted to its connected PCC node is accurate. The AC power flow error comes from the AC power grid connected to the voltage station, because the acquisition of the state information of the voltage station relies on the DC power grid power flow calculation results, and the fast linear power flow algorithm of the DC power grid will produce errors, thus affecting the accuracy of the state information of the voltage station.

[0121] The computational efficiency of the improved power flow algorithm of the present invention compared with the traditional AC / DC power flow algorithm is shown in the following table

[0122] Comparison of operation efficiency (single-point voltage control)

[0123]

[0124]

[0125] Comparison of operation efficiency (multi-point voltage droop)

[0126]

[0127] As can be seen from the above two tables, this algorithm does not require loops, which greatly reduces the number of iterations of the DC power grid and AC power grid power flow, as well as the number of calculations of the power station and voltage station. In addition, for interconnected power grids that solve multi-point voltage droop control, the calculation efficiency of the present invention is more significant. Because the present invention uses linear fast power flow calculations for DC power grids, even if multi-point droop control is used, the dimension of the linear equation will not increase, and it can still be solved in one step. For the power flow algorithm of traditional DC power grids, when multi-point droop control is used, the nonlinearity of the power flow model increases, resulting in an increase in solution time.

[0128] Therefore, the rapidity of the algorithm of the present invention benefits from two points:

[0129] First, realize decoupled calculation without loop.

[0130] Second, linear fast DC power flow calculation is adopted for DC power grid.

[0131] It is worth noting that as the number of nodes in the DC system or AC system increases, the advantages of the present invention will become more obvious. Because there is no need for cyclic calculation, only a single AC power flow or DC power flow calculation is required, and the calculation efficiency will not decrease due to the accumulation of cycles, so the calculation efficiency will become more significant as the power grid expands. In addition, the calculation burden each time is only a single AC power grid or DC power grid or converter station, and the memory requirement for the computer is small.

[0132] The general flexibility of the present invention is high, and a "natural" decoupling effect is achieved. The AC power grid flow, converter station flow, and DC power grid flow can be calculated in sequence according to the steps, without adding correction links, and accurate flow results can be obtained each time the calculation is performed. In addition, the present invention does not change the interconnected power grid and converter station structure, takes into account different control modes and detailed loss models of VSC, and does not introduce new variables, which further improves the general flexibility of the algorithm, making it widely applicable to the flow calculation of multi-terminal DC partitioned interconnected power grids.

[0133] At the same time, the algorithm is easy to program and has high algorithm expansion and portability. The AC power flow calculation is consistent with the traditional algorithm, and a toolkit or more advanced AC power flow calculation can be used as needed. The linear power flow algorithm for DC power grid is easy to program, and only two sets of matrix inversions are needed to obtain the power flow calculation results. The power station power flow is based on the basic circuit principle; the voltage station power flow is a low-order nonlinear equation solution, which can be solved using a general solution function or a custom Newton method.

[0134] At this point, the task of the improved power flow algorithm for a multi-terminal DC partitioned interconnected power grid proposed in the present invention is fully completed.

Claims

1. An improved power flow algorithm for a multi-terminal DC zoned interconnected power grid, characterized by: The following steps are involved: A. Input the status information of the PCC node of the power station into the AC power grid connected to the power station to perform AC power flow calculation; B. Perform power station power flow calculation based on the AC power flow calculation results; C. Perform fast linear power flow calculation on the DC grid based on the power station power flow calculation results; D. Perform voltage station power flow calculation based on DC power flow calculation results; E. Input the status information of the PCC node of the voltage station into the AC power grid connected to the voltage station to perform AC power flow calculation.

2. The improved power flow algorithm for a multi-terminal DC zoned interconnected power grid according to claim 1 is characterized in that: Step A inputs the status information of the PCC node of the power station into the AC power grid connected to the power station to perform AC power flow calculation. The specific process is as follows: First, the AC power flow calculation lacks the PCC node status information of the VSC converter station, while the PCC node status information of the power station is complete; Then, for the multi-terminal DC zoned interconnected power grid, the power flow calculation is first performed on the AC power grid connected to the power station; Finally, the AC power flow calculation model is established and the AC power flow calculation is performed.

3. The improved power flow algorithm for a multi-terminal DC zoned interconnected power grid according to claim 1 is characterized in that: The PCC node status information consists of active power and reactive power, or active power and voltage amplitude.

4. The improved power flow algorithm for a multi-terminal DC zoned interconnected power grid according to claim 1 is characterized in that: Step B performs power station power flow calculation based on the AC power flow calculation results. The specific process is as follows: First, after the AC power flow calculation, the voltage amplitude and phase angle, or reactive power and voltage phase angle, of the PCC node of the power station are obtained; Then, the power station power flow calculation is performed by combining the AC power flow calculation results with the known status information of the power station PCC node; Finally, the active power injected into the DC grid by the power station is obtained.

5. The improved power flow algorithm for a multi-terminal DC zoned interconnected power grid according to claim 1 is characterized in that: Step C performs fast linear power flow calculation on the DC grid according to the power station power flow calculation results. The specific process is as follows: Firstly, a fast linear power flow model of the DC grid is established; Then, after obtaining the active power injected into the DC grid by the power station, the fast linear power flow model is used to calculate the fast linear power flow of the DC grid; Finally, the DC power grid flow calculation results are obtained.

6. The improved power flow algorithm for a multi-terminal DC zoned interconnected power grid according to claim 1, characterized in that: Step D performs voltage station power flow calculation based on the DC power flow calculation results. The specific process is as follows: First, after the power flow of the DC grid is solved, the active power injected into the DC grid by the voltage station is obtained; Then, the active power injected into the AC grid by the voltage station is obtained through the voltage station power flow model; Finally, the voltage station power flow model is established and the voltage station power flow calculation is performed.

7. The improved power flow algorithm for a multi-terminal DC zoned interconnected power grid according to claim 2, characterized in that: Step E inputs the status information of the voltage station PCC node into the AC power grid connected to the voltage station to perform AC power flow calculation. The specific process is as follows: First, after the voltage station power flow is solved, the status information of the PCC node of the voltage station is obtained; Then, the power flow calculation is performed on the AC power grid connected to the voltage station.

8. The improved power flow algorithm for a multi-terminal DC zoned interconnected power grid according to claim 7, characterized in that: The AC power flow calculation model in step A is the same as that in step E.

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