AC / DC hybrid power grid decoupling power flow fast algorithm

Abstract

The invention discloses an AC / DC hybrid power grid decoupling power flow fast algorithm. The algorithm comprises the following steps: carrying out per-unit processing on an AC / DC hybrid power grid; taking a power station instruction as a convergence criterion, carrying out rapid direct current power flow calculation, backstepping the power station coupling power flow, and determining a direct current power flow calculation result; carrying out load flow calculation on a voltage station coupling part, and determining active power, reactive power or a voltage module value of a PCC point at the voltage station coupling part; and inputting the active power, the reactive power or the voltage module value of the PCC point into an alternating current system, and carrying out alternating current load flow calculation. According to the method, AC-DC power flow decoupling calculation is realized without changing a hybrid power grid structure and a converter station control mode, without introducing new variables, considering a detailed converter station loss model and a converter station coupling model and under different converter station control modes, the number of iterations of hybrid power grid power flow calculation is greatly reduced on the premise of ensuring the power flow calculation accuracy, and the power flow calculation efficiency is improved. The load flow calculation method can be widely applied to load flow calculation work of the alternating-current and direct-current hybrid power grid.

Description

Technical Field

[0001] The invention belongs to the field of AC / DC hybrid power grid power flow calculation, and in particular relates to a fast algorithm for decoupling power flow of an AC / DC hybrid power grid. Background Art

[0002] my country's renewable energy is developing rapidly. In 2023, the cumulative installed capacity of renewable energy in my country exceeded 1.5 billion kilowatts, accounting for 51.9% of the country's total installed power generation capacity and nearly 40% of the world's renewable energy installed power generation capacity. The grid connection of renewable energy needs to rely on the DC system. The grid connection of renewable energy based on voltage source converter VSC (voltage source converter) can improve the efficiency and controllability of renewable energy grid connection. Therefore, the DC grid based on VSC is an effective solution for large-scale renewable energy grid connection and increasing the penetration rate of new energy.

[0003] So far, several representative multi-terminal DC transmission projects have been put into operation at home and abroad, including the Nan'ao three-terminal flexible DC demonstration project, the Zhejiang Zhoushan five-terminal flexible DC demonstration project, the Zhangbei four-terminal DC project, and the three-terminal Trans Bay Cable DC transmission project in the United States. Therefore, with the continuous development of new power systems, AC / DC hybrid power grids containing VSCs are the development trend of future power grids.

[0004] Power flow calculation is a necessary condition for studying and analyzing the steady-state and transient characteristics of AC / DC hybrid power grids, and has important theoretical research and practical application value. The existing AC / DC power flow calculation mainly includes the alternating iteration method and the unified iteration method.

[0005] The unified iteration method needs to completely calculate the Jacobian matrix of the entire AC / DC hybrid power grid, which requires a huge amount of calculation. In addition, in the process of forming the Jacobian matrix, the unified iteration method needs to make significant modifications to the Jacobian matrix of the AC system, so it has poor inheritance to the existing AC system calculation program. Compared with the unified iteration method, the alternating iteration method solves equations with lower dimensions and less calculation, and has better inheritance to the existing AC system power flow program, and can flexibly modify the AC / DC system structure. However, the alternating iteration method requires alternating power flow calculations of the AC and DC subsystems, and each alternation requires repeated iterations of the DC system, AC system, and AC / DC coupling, which results in a large number of iterations for the alternating iteration method and longer calculation time.

[0006] By studying the decoupling algorithm of AC and DC power flow, it is possible to calculate AC and DC power flows separately without alternating, and improve the calculation efficiency by calculating AC, DC and coupling power flows separately. However, the current AC and DC decoupling algorithms are based on changing the control mode of the converter, hybrid grid structure, ignoring the detailed losses of the converter, etc., and there is still room for improvement in calculation efficiency.

[0007] In view of the above situation, the present invention discloses a fast algorithm for decoupling power flow in an AC / DC hybrid power grid. Summary of the invention

[0008] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a fast algorithm for decoupling power flow of an AC / DC hybrid power grid.

[0009] The technical solution of the present invention is: a fast algorithm for decoupling power flow of AC / DC hybrid power grid, comprising the following steps: A. Perform standard processing on AC / DC hybrid power grid; B. Using the power station command as the convergence criterion, perform fast DC power flow calculation, reverse the power station coupling power flow, and determine the DC power flow calculation results; C. Carry out power flow calculation at the voltage station coupling point to determine the active power, reactive power or voltage modulus value at the PCC point at the voltage station coupling point; D. Input the active power, reactive power or voltage modulus of the PCC point into the AC system to perform AC power flow calculation.

[0010] Furthermore, step A performs per-unit processing on the AC / DC hybrid power grid, and the specific process is as follows: Firstly, the internal base value of the DC grid is taken as the rated voltage of the DC grid and the rated power of the DC grid; Then, the internal base value of the AC grid is used as the rated voltage of the AC grid and the rated power of the AC grid; Finally, the base value at the coupling point between the power station and the voltage station is taken as the base value of the AC power grid.

[0011] Furthermore, in step B, a fast DC power flow calculation is performed, and the specific process is as follows: First, assume the active power of the power station PCC point P sref Inject power into the DC side of the power station P dc ; Then, fast DC power flow calculation is performed. The calculation expression of fast DC power flow calculation is as follows: ; in, A is the coefficient matrix containing the unified control characteristics of the converter station; U is the voltage deviation at each node in the DC grid; B Related to the reference power, reference voltage and droop coefficient of each node; Finally, the above calculation expression is a linear equation. By converting the nonlinear algebraic equation of DC power flow into a linear algebraic equation, a fast DC power flow algorithm is obtained, which can realize direct solution of DC power grid power flow without iteration.

[0012] Furthermore, the fast DC power flow calculation is specifically carried out as follows: ; in, n Indicates the number of nodes in the DC grid; β It represents the inverse of the droop coefficient of each node. The droop coefficient of the voltage station is ∞, the droop coefficient of the power station is 0, and the droop coefficient of the DC node without the converter station is 0; y ij Indicates the DC grid i Node to j Admittance of node branches; ; Among them, △ U i * Indicates the DC grid i The difference between a node voltage reference value and a node voltage base value; P i * represents the injected power of the i-th node; T represents transpose; and ; in, P dc,i For the i Active power injected from the AC side to the DC side by each node; P gen,i For the i The active power generated by the generator connected to each node; P load,i For the i Active power of load on each node; P dc,i For voltage stations and non-converter station nodes, this value is 0. For power stations, this value is the power station active power instruction for the first iteration. P s .

[0013] Furthermore, in step B, the voltage of each node of the DC grid and the injected active power are solved by fast DC power flow calculation, and the power station P dc,i Assume that the active power command of the power station P s It is not the active power injected from the AC side to the DC side by the actual power station. It is necessary to reverse the power flow at the coupling point of the power station to obtain the power at the PCC point, and iterate with the active power command of the power station as the convergence criterion.

[0014] Furthermore, step B reverses the power flow at the coupling point of the power station. The specific process is as follows: First, the loss model of the converter station is as follows: ; in, I c is the AC current flowing through the converter station; the coefficient a , b , c is the loss coefficient of the converter station; Then, according to the DC power flow calculation results, the power station power flow is reversed as shown in the following formula: ; in, abs Indicates taking the absolute value; P c Indicates the active power transmitted by VSC to the AC side; Q sref Indicates the reactive power command of the power station; U sref Indicates the voltage command of the power station; μ is the DC voltage utilization; M is the modulation ratio; | U c |Indicates the voltage at the AC side outlet of the power station VSC U c The modulus value of U dc represents the DC side voltage of the power station obtained by fast DC power flow solution, so U c The modulus value will change with the results of DC power flow; x Represents the variables to be determined. There are two variables to be determined, namely, the voltage at the PCC point of the power station U s The modulus of | U s | and angle δ s ; If the reactive power control of the power station is fixed Q s Then the second equation is based on the former. If the reactive power control of the power station is constant U s Then the second equation shall prevail over the latter; Finally, after inverting the power station flow, the power of the PCC point is solved P s .

[0015] Furthermore, step B determines the DC power flow calculation result, and the specific process is as follows: First, power P s Value and actual power station active power command P srefThere is a deviation. According to the deviation, update the power station according to the following formula P dc ,Right now: ; Then, the updated P dc Re-enter the value of into the fast DC power flow calculation and repeat step B until the power P s Reach convergence accuracy, that is: ; in, ɛ Indicates the convergence accuracy, which can be selected according to the accuracy requirements; Finally, the DC power flow calculation results were determined.

[0016] Furthermore, step C performs power flow calculation at the voltage station coupling point to determine the active power, reactive power or voltage modulus of the PCC point at the voltage station coupling point. The specific process is as follows: First, the formula for calculating the power flow at the voltage station coupling is the same as the reverse power station power flow, as shown below: ; in, abs Indicates taking the absolute value; P c Indicates the active power transmitted by VSC to the AC side; Q sref Indicates the reactive power instruction of the voltage station; U sref Indicates the voltage command of the voltage station; μ is the DC voltage utilization; M is the modulation ratio; | U c |Indicates the voltage at the AC side outlet of the voltage station VSC U c The modulus value, U dc It represents the DC side voltage of the voltage station obtained by fast DC power flow solution; x Indicates the variable to be determined; Then, by using the above formula, we can get the PCC point at the voltage station coupling. P s and Q s .

[0017] Furthermore, the variable to be determined x There are two variables to be determined, namely the voltage at the voltage station PCC point U s The modulus of | U s| and angle δ s , such as voltage station reactive power control selection fixed Q s Then the second equation shall prevail over the former. U s The second equation is then based on the latter.

[0018] The beneficial effects of the present invention are as follows: The present invention realizes AC / DC power flow decoupling calculation without changing the AC / DC hybrid power grid structure and converter station control mode, without introducing new variables, and taking into account a detailed converter station loss model, a converter station coupling point model, and different converter station control modes.

[0019] Under the premise of ensuring the accuracy of power flow calculation, the present invention greatly reduces the number of iterations of hybrid power grid power flow calculation, improves the operation efficiency, has clear algorithm logic, ensures the convenience of program design and the general flexibility of algorithm expansion and transplantation, and can be widely used in AC / DC hybrid power grid power flow calculation work. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the method of the present invention; Figure 2 It is an iterative flow chart of step B in the present invention; Figure 3 It is the converter station coupling model in the present invention; Figure 4 It is a topological diagram of the AC / DC hybrid power grid in the present invention. DETAILED DESCRIPTION

[0021] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and embodiments: like Figures 1 to 4 As shown, a fast algorithm for decoupling power flow in an AC / DC hybrid power grid includes the following steps: A. Perform standard processing on AC / DC hybrid power grid; B. Using the power station command as the convergence criterion, perform fast DC power flow calculation, reverse the power station coupling power flow, and determine the DC power flow calculation results; C. Carry out power flow calculation at the voltage station coupling point to determine the active power, reactive power or voltage modulus value at the PCC point at the voltage station coupling point; D. Input the active power, reactive power or voltage modulus of the PCC point into the AC system to perform AC power flow calculation.

[0022] Step A performs per-unit processing on the AC / DC hybrid power grid. The specific process is as follows: Firstly, the internal base value of the DC grid is taken as the rated voltage of the DC grid and the rated power of the DC grid; Then, the internal base value of the AC grid is used as the rated voltage of the AC grid and the rated power of the AC grid; Finally, the base value at the coupling point between the power station and the voltage station is taken as the base value of the AC power grid.

[0023] In step B, fast DC power flow calculation is performed. The specific process is as follows: First, assume the active power of the power station PCC point P sref Inject power into the DC side of the power station P dc ; Then, fast DC power flow calculation is performed. The calculation expression of fast DC power flow calculation is as follows: ; in, A is the coefficient matrix containing the unified control characteristics of the converter station; U is the voltage deviation at each node in the DC grid; B Related to the reference power, reference voltage and droop coefficient of each node; Finally, the above calculation expression is a linear equation. By converting the nonlinear algebraic equation of DC power flow into a linear algebraic equation, a fast DC power flow algorithm is obtained, which can realize the direct solution of DC power grid power flow without iteration. The specific development of fast DC power flow calculation is as follows: ; in, n Indicates the number of nodes in the DC grid; β It represents the inverse of the droop coefficient of each node. The droop coefficient of the voltage station is ∞, the droop coefficient of the power station is 0, and the droop coefficient of the DC node without the converter station is 0; y ij Indicates the DC grid i Node to j Admittance of node branches; ; Among them, △ U i * Indicates the DC grid i The difference between a node voltage reference value and a node voltage base value; P i * represents the injected power of the i-th node; T represents transpose, and ; in, P dc,i For the i Active power injected from the AC side to the DC side by each node;P gen,i For the i The active power generated by the generator connected to each node; P load,i For the i Active power of load on each node; P dc,i For voltage stations and non-converter station nodes, this value is 0. For power stations, this value is the power station active power instruction for the first iteration. P s .

[0024] In step B, the voltage of each node of the DC grid and the injected active power are obtained by fast DC power flow calculation, and the power station P dc,i Assume that the active power command of the power station P s It is not the active power injected from the AC side to the DC side by the actual power station. It is necessary to reverse the power flow at the coupling point of the power station to obtain the power at the PCC point, and iterate with the active power command of the power station as the convergence criterion.

[0025] Step B reverses the power flow at the power station coupling point. The specific process is as follows: First, the loss model of the converter station is as follows: ; in, I c is the AC current flowing through the converter station; the coefficient a , b , c is the loss coefficient of the converter station; Then, according to the DC power flow calculation results, the power station power flow is reversed as shown in the following formula: ; in, abs Indicates taking the absolute value; P c Indicates the active power transmitted by VSC to the AC side; Q sref Indicates the reactive power command of the power station; U sref Indicates the voltage command of the power station; μ is the DC voltage utilization; M is the modulation ratio; | U c |Indicates the voltage at the AC side outlet of the power station VSC U c The modulus value of U dc represents the DC side voltage of the power station obtained by fast DC power flow solution, so Uc The modulus value will change with the results of DC power flow; x Represents the variables to be determined. There are two variables to be determined, namely, the voltage at the PCC point of the power station U s The modulus of | U s | and angle δ s ; If the reactive power control of the power station is fixed Q s Then the second equation is based on the former. If the reactive power control of the power station is constant U s Then the second equation shall prevail over the latter; Finally, after inverting the power station flow, the power of the PCC point is solved P s .

[0026] Step B determines the DC power flow calculation result. The specific process is as follows: First, power P s Value and actual power station active power command P sref There is a deviation. According to the deviation, update the power station according to the following formula P dc ,Right now: ; Then, the updated P dc Re-enter the value of into the fast DC power flow calculation and repeat step B until the power P s Reach convergence accuracy, that is: ; in, ɛ Indicates the convergence accuracy, which can be selected according to the accuracy requirements; Finally, the DC power flow calculation results were determined.

[0027] Step C performs power flow calculation at the voltage station coupling point to determine the active power, reactive power or voltage modulus of the PCC point at the voltage station coupling point. The specific process is as follows: First, the formula for calculating the power flow at the voltage station coupling is the same as the reverse power station power flow, as shown below: ; in, abs Indicates taking the absolute value; P c Indicates the active power transmitted by VSC to the AC side; Q sref Indicates the reactive power instruction of the voltage station;U sref Indicates the voltage command of the voltage station; μ is the DC voltage utilization; M is the modulation ratio; | U c |Indicates the voltage at the AC side outlet of the voltage station VSC U c The modulus value, U dc It represents the DC side voltage of the voltage station obtained by fast DC power flow solution; x Indicates the variable to be determined; Then, by using the above formula, we can get the PCC point at the voltage station coupling. P s and Q s .

[0028] The variable to be determined x There are two variables to be determined, namely the voltage at the voltage station PCC point U s The modulus of | U s | and angle δ s , such as voltage station reactive power control selection fixed Q s Then the second equation shall prevail over the former. U s The second equation is then based on the latter.

[0029] Specifically, step D inputs the active power, reactive power or voltage modulus of the PCC point into the AC system to perform AC power flow calculation. The specific process is as follows: First, if the reactive power is fixed in the power station reactive control, the active power and reactive power of all the PCC points of the power station can be determined through the above steps; if the reactive power control of the power station is fixed in the voltage modulus, the active power and voltage modulus of all the PCC points of the power station can be determined through the above steps; Then, if the voltage station reactive power control selects fixed reactive power, the active power and reactive power of all voltage station PCC points can be determined through the above steps; if the voltage station reactive power control selects fixed voltage modulus, the active power and voltage modulus of all voltage station PCC points can be determined through the above steps; Finally, the information of the PCC point is input into the AC system, and MATPOWER is called to calculate the AC system power flow using the Newton-Raphson method.

[0030] Specifically, in step B, the rated operating loss of the two (three) level converter station is usually about 3%, while the loss of the MMC converter station is about 1%, so the power station Psref and P dc The numerical values ​​of are not much different, so the number of iterations required for step B of the present invention is small. Moreover, because the present invention adopts a fast DC power flow algorithm, even if step B is iterated, the time consumed is very short. Example

[0031] This embodiment uses an AC / DC hybrid power grid to compare and analyze the decoupled power flow fast algorithm proposed in the present invention and the traditional AC / DC power flow algorithm. The topology diagram of the converter station coupling point used is as follows: Figure 3 As shown in the figure, the converter station coupling consists of filter capacitors, transformers, and reactors; the AC / DC hybrid power grid simulation topology is shown in Figure 4 As shown in FIG, the topology diagram is a three-terminal AC / DC hybrid power grid formed by three IEEE 33-node AC systems and one 7-node DC system.

[0032] A fast algorithm for decoupling power flow in an AC / DC hybrid power grid includes the following steps: A. Perform standard processing on AC / DC hybrid power grid; B. Using the power station command as the convergence criterion, perform fast DC power flow calculation, reverse the power station coupling power flow, and determine the DC power flow calculation results; C. Carry out power flow calculation at the voltage station coupling point to determine the active power, reactive power or voltage modulus value at the PCC point at the voltage station coupling point; D. Input the active power, reactive power or voltage modulus of the PCC point into the AC system to perform AC power flow calculation.

[0033] Firstly, the AC / DC hybrid power grid is standardized. The power base value at the coupling point between the AC measurement and the converter station is 100MVA, and the voltage base value is 12.66kV; the power base value at the DC side is 100MW, and the voltage base value is 10kV.

[0034] At the same time, it is stipulated that the positive direction of injection into the AC grid is used as the reference direction at the coupling point between the AC measurement and the converter station, and the positive direction of injection into the DC grid is used as the reference direction on the DC side.

[0035]

[0036] The present invention will perform power flow calculation and comparative analysis from two control modes: single-point voltage control and multi-point droop control.

[0037] When single-point voltage control is adopted, the converter station control parameters are shown in the following table

[0038] As can be seen from the table above, when single-point voltage control is adopted, VSC1 is the voltage station, which controls the voltage of the DC node to which it is connected. Udc and the reactive power at the PCC point Q s VSC2 and VSC3 control the active power of the PCC point to which they are connected. P s and reactive power Q s .

[0039] When multi-point voltage droop control is adopted, the converter station control parameters are shown in the following table

[0040] 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 of the PCC nodes to which they are connected. Q s , and controls the voltage of the DC node to which it is connected U dc and active power P dc The following relations are satisfied: ; in, P dcref Indicates the DC side power reference value, U dcref Indicates the DC voltage reference value.

[0041] Finally, the error of the fast algorithm for decoupling power flow of the AC / DC hybrid power grid of the present invention is shown in the following table:

[0042] As can be seen from the above table, the errors finally obtained by the present invention are all less than 0.03%, which is extremely small, so the results of the power flow calculation are reliable. The reason for the error in the present invention is that the high-order voltage change variation is ignored when using the fast DC power flow algorithm, so the DC power flow calculation will produce errors, and there will also be errors when the DC power grid transmits PCC point information to the AC power grid. At the same time, the error is related to the DC network loss. As the network loss rate increases, the error will increase, but in fact the network loss rate of the DC network is approximately within 2%, so the error is acceptable.

[0043] The computational efficiency of the decoupled power flow fast algorithm of the present invention is compared with the traditional AC / DC power flow algorithm as shown in the following table

[0044] It can be seen from the above two tables that the decoupled power flow fast algorithm proposed in the present invention requires much fewer iterations and less calculation time than the traditional AC / DC power flow algorithm. P s andP dc The values ​​are not much different, so the number of cycles of the decoupled power flow fast algorithm is small, and the fast DC power flow algorithm is used, and only one fast iteration is required for each cycle. The present invention only needs to perform a small number of loop iterations at step B, and only fast DC power flow calculation is performed in each cycle, so it takes less time.

[0045] As the number of nodes in the DC system increases, the superiority of the fast DC power flow algorithm used in the present invention will become more obvious. As the number of nodes in the AC system increases, the number of cycles of the present invention will not change, because the present invention realizes the decoupling of the AC system and the DC system and solves them separately, and the solution time will only increase monotonically with the increase of the single AC system solution time. Therefore, compared with the traditional AC / DC power flow algorithm, the computing efficiency of the present invention will be more significant as the scale of the AC / DC hybrid power grid expands.

[0046] The present invention realizes the decoupling calculation of AC and DC power flow without changing the hybrid power grid structure and converter station control mode, without introducing new variables, and taking into account the detailed converter station loss model, converter station coupling point model, and different converter station control modes. The numerical simulation results show that compared with the traditional AC and DC power flow calculation method, the proposed method greatly reduces the number of iterations of hybrid power grid power flow calculation and improves the calculation efficiency while ensuring the accuracy.

[0047] The present invention ensures the convenience of program design and the general flexibility of algorithm expansion and transplantation, etc. The AC system and DC system can be modified according to the needs, and different AC power flow algorithms and DC power flow algorithms can be used, which can be widely used in AC / DC hybrid power grid planning.

[0048] The tasks of the fast algorithm for decoupling power flow of an AC / DC hybrid power grid proposed by the present invention are all completed.

Claims

1. A fast algorithm for decoupling power flow in an AC / DC hybrid power grid, characterized by: The following steps are involved: A. Perform standard processing on AC / DC hybrid power grid; B. Using the power station command as the convergence criterion, perform fast DC power flow calculation, reverse the power station coupling power flow, and determine the DC power flow calculation results; C. Carry out power flow calculation at the voltage station coupling point to determine the active power, reactive power or voltage modulus value at the PCC point at the voltage station coupling point; D. Input the active power, reactive power or voltage modulus of the PCC point into the AC system to perform AC power flow calculation.

2. The fast algorithm for decoupling power flow in an AC / DC hybrid power grid according to claim 1, characterized in that: Step A performs per-unit processing on the AC / DC hybrid power grid. The specific process is as follows: Firstly, the internal base value of the DC grid is taken as the rated voltage of the DC grid and the rated power of the DC grid; Then, the internal base value of the AC grid is used as the rated voltage of the AC grid and the rated power of the AC grid; Finally, the base value at the coupling point between the power station and the voltage station is taken as the base value of the AC power grid.

3. The fast algorithm for decoupling power flow in an AC / DC hybrid power grid according to claim 1, characterized in that: In step B, fast DC power flow calculation is performed. The specific process is as follows: First, assume the active power of the power station PCC point P sref Inject power into the DC side of the power station P dc ; Then, fast DC power flow calculation is performed. The calculation expression of fast DC power flow calculation is as follows: ； in, A is the coefficient matrix containing the unified control characteristics of the converter station; U is the voltage deviation at each node in the DC grid; B Related to the reference power, reference voltage and droop coefficient of each node; Finally, the above calculation expression is a linear equation. By converting the nonlinear algebraic equation of DC power flow into a linear algebraic equation, a fast DC power flow algorithm is obtained, which can realize direct solution of DC power grid power flow without iteration.

4. The fast algorithm for decoupling power flow in an AC / DC hybrid power grid according to claim 3 is characterized by: The specific development of fast DC power flow calculation is as follows: ； in, n Indicates the number of nodes in the DC grid; β It represents the inverse of the droop coefficient of each node. The droop coefficient of the voltage station is ∞, the droop coefficient of the power station is 0, and the droop coefficient of the DC node without the converter station is 0; y ij Indicates the DC grid i Node to j Admittance of node branches; ； Among them, △ U i * Indicates the DC grid i The difference between a node voltage reference value and a node voltage reference value; P i * represents the injected power of the ith node, T represents transpose; and ； in, P dc,i For the i Active power injected from the AC side to the DC side by each node; P gen,i For the i The active power generated by the generator connected to each node; P load,i For the i Active power of load on each node; P dc,i For voltage stations and non-converter station nodes, this value is 0. For power stations, this value is the power station active power instruction for the first iteration. P s .

5. The fast algorithm for decoupling power flow in an AC / DC hybrid power grid according to claim 4, characterized in that: In step B, the voltage of each node of the DC grid and the injected active power are obtained by fast DC power flow calculation, and the power station P dc,i Assume that the active power command of the power station P s It is not the active power injected from the AC side to the DC side by the actual power station. It is necessary to reverse the power flow at the coupling point of the power station to obtain the power at the PCC point, and iterate with the active power command of the power station as the convergence criterion.

6. The fast algorithm for decoupling power flow in an AC / DC hybrid power grid according to claim 1, characterized in that: Step B reverses the power flow at the power station coupling point. The specific process is as follows: First, the loss model of the converter station is as follows: ； in, I c is the AC current flowing through the converter station; the coefficient a , b , c is the loss coefficient of the converter station; Then, according to the DC power flow calculation results, the power station power flow is reversed as shown in the following formula: ； in, abs Indicates taking the absolute value; P c Indicates the active power transmitted by VSC to the AC side; Q sref Indicates the reactive power command of the power station; U sref Indicates the voltage command of the power station; μ is the DC voltage utilization; M is the modulation ratio; | U c |Indicates the voltage at the AC side outlet of the power station VSC U c The modulus value of U dc represents the DC side voltage of the power station obtained by fast DC power flow solution, so U c The modulus value will change with the results of DC power flow; x Represents the variables to be determined. There are two variables to be determined, namely, the voltage at the PCC point of the power station U s The modulus of | U s | and angle δ s ; If the reactive power control of the power station is fixed Q s Then the second equation is based on the former. If the reactive power control of the power station is constant U s Then the second equation shall prevail over the latter; Then, after inverting the power station flow, the power of the PCC point is solved P s .

7. The fast algorithm for decoupling power flow in an AC / DC hybrid power grid according to claim 6, characterized in that: Step B determines the DC power flow calculation result. The specific process is as follows: First, power P s Value and actual power station active power command P sref There is a deviation. According to the deviation, update the power station according to the following formula P dc ,Right now: ； Then, the updated P dc Re-enter the value of into the fast DC power flow calculation and repeat step B until the power P s Reach convergence accuracy, that is: ； in, ɛ Indicates the convergence accuracy, which can be selected according to the accuracy requirements; Finally, the DC power flow calculation results were determined.

8. The fast algorithm for decoupling power flow in an AC / DC hybrid power grid according to claim 1, characterized in that: Step C performs power flow calculation at the voltage station coupling point to determine the active power, reactive power or voltage modulus of the PCC point at the voltage station coupling point. The specific process is as follows: First, the formula for calculating the power flow at the voltage station coupling is the same as the reverse power station power flow, as shown below: ； in, abs Indicates taking the absolute value; P c Indicates the active power transmitted by VSC to the AC side; Q sref Indicates the reactive power instruction of the voltage station; U sref Indicates the voltage command of the voltage station; μ is the DC voltage utilization; M is the modulation ratio; | U c |Indicates the voltage at the AC side outlet of the voltage station VSC U c The modulus value, U dc It represents the DC side voltage of the voltage station obtained by fast DC power flow solution; x Indicates the variable to be determined; Then, by using the above formula, we can get the PCC point at the voltage station coupling. P s and Q s .

9. The fast algorithm for decoupling power flow in an AC / DC hybrid power grid according to claim 8, characterized in that: The variable to be determined x There are two variables to be determined, namely the voltage at the voltage station PCC point U s The modulus of | U s | and angle δ s , such as voltage station reactive power control selection fixed Q s Then the second equation shall prevail over the former. U s The second equation is then based on the latter.

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