CN111799800A - AC-DC hybrid power distribution network load flow calculation method - Google Patents
AC-DC hybrid power distribution network load flow calculation method Download PDFInfo
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- H—ELECTRICITY
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Abstract
A load flow calculation method for an alternating current-direct current hybrid power distribution network belongs to the field of power grid operation scheduling. Aiming at a power distribution network in an area, determining a topological structure of the whole power distribution network and determining a node type of the power distribution network; constructing an alternating current-direct current hybrid power distribution network model taking a multi-port electric energy router as a core, and setting a series of parameters for the model; carrying out load flow calculation based on a Newton method; calculating to obtain the load flow of the whole alternating current-direct current power distribution network comprising the multi-port electric energy router, and simultaneously obtaining the voltage of each node; and further, the line loss and the multi-port electric energy router loss can be obtained. The problem that a traditional load flow calculation method cannot be applied to a novel alternating current-direct current hybrid power distribution network including new energy power generation equipment access can be effectively solved; aiming at the current conversion links of the AC/DC power distribution network with different voltage grades, a novel electric energy router in the region is adopted for electric energy routing, and the real-time information flow controls the power flow. The method can be widely applied to the field of power flow calculation of power grid operation scheduling and alternating current-direct current hybrid power distribution networks.
Description
Technical Field
The invention belongs to the field of power grid operation scheduling, and particularly relates to a load flow calculation method for an alternating current-direct current hybrid power distribution network.
Background
In recent years, in order to alleviate the energy crisis and reduce the pollution of industrial emission, a large number of distributed new energy devices are incorporated into the power grid, but these new energy power supplies have the characteristics of geographical dispersibility, intermittence, randomness and the like, so in order to reduce the distribution pressure of the power grid and increase the utilization rate of renewable energy, a large number of energy storage devices are added into the power grid to provide energy buffering, and meanwhile, the conventional power generation mode is also being changed into a centralized and distributed coexistence mode. Due to the addition of new energy direct current loads such as electric automobiles and the like, the management of electric energy becomes more difficult, and the traditional power distribution system of the power system can not meet the requirement any more.
With the extensive application of flexible interconnection projects based on power electronic technology to the pilot point demonstration of various voltage levels in power distribution systems, power distribution systems are gradually evolving from traditional single alternating current power distribution systems to alternating current and direct current hybrid intelligent flexible power distribution systems.
And the flexible power distribution network is adopted, so that the access and the high-efficiency operation of various distributed power supplies, energy storage and flexible loads can be met. Meanwhile, the flexible interconnection technology enables the direct-current power distribution network and the alternating-current power distribution network to run in a mixed mode better. At present, the basic form of energy internet in each country comprises an alternating current bus and a direct current bus, an alternating current bus network is mainly used for meeting the requirements of various traditional alternating current load electric equipment, and a direct current bus network is used for accessing a distributed power supply, a direct current load, an energy storage device, various variable frequency loads and the like. Therefore, load flow calculation for the ac/dc hybrid power distribution network becomes an important content of current research.
In the multilevel alternating current-direct current power distribution network, the distributed power supply is connected into the low-voltage direct current power distribution network in a direct current mode, a large number of links from direct current to alternating current can be omitted, a large amount of electric energy is saved, meanwhile, tracking of phase and frequency is not needed, and controllability and reliability are greatly improved. Direct current is an ideal access form of a distributed power supply, and is more and more emphasized by people in recent years, however, an alternating current power distribution network is also a main form of a current power distribution network, and alternating current access is also an important part of distributed power supply grid connection, so that an alternating current and direct current mixed power distribution network is an important power distribution network existence form in a future period of time. A large number of distributed new energy power sources are merged into a power grid, so that a low-voltage alternating-current power distribution network and a low-voltage direct-current power distribution network play more and more various and important roles in the power distribution network, and a medium-voltage direct-current power distribution network can be used for medium-distance and long-distance power transmission. At present, the basic form of energy internet in each country comprises an alternating current bus and a direct current bus, an alternating current bus network is mainly used for meeting the requirements of various traditional alternating current load electric equipment, and a direct current bus network is used for accessing a distributed power supply, a direct current load, an energy storage device, various variable frequency loads and the like.
The alternating current and direct current hybrid power distribution network load flow calculation method mainly comprises a unified iteration method and an alternate iteration method. Wherein:
(1) the unified iteration method has good convergence, less iteration times and easy realization, and the direct current part and the alternating current part use the same algorithm, but have the following defects: (a) the method cannot be combined with the existing commercial software, and the compiling difficulty is high; (b) after each iteration, the jacobian matrix needs to be recalculated, so that the calculation amount is relatively large.
(2) The alternating iteration method has the advantages that the interface with the existing commercial software is easy, the programming is simple, the calculation speed is high, and different algorithms can be used for the direct current part and the alternating current part; however, there are the following problems: (a) in the process of load flow calculation, the loss of a converter and the injection power of a balance converter station cannot be accurately known in single load flow calculation, so that the number of iterations is increased; (b) the requirement on the initial value setting of an alternating current and direct current system is high, the convergence is relatively poor, and the oscillation and the non-convergence of the power flow solution are easily caused.
Disclosure of Invention
The invention aims to provide a method for calculating the load flow of an alternating current-direct current hybrid power distribution network. The method comprises the steps of firstly carrying out load flow calculation on a low-voltage distribution network to obtain electric energy injection data, then respectively carrying out load flow calculation on medium-voltage distribution networks, and finally obtaining load flow calculation results of the distribution networks in the whole area. The problem that a traditional load flow calculation method cannot be applied to a novel alternating current-direct current hybrid power distribution network including new energy power generation equipment access can be effectively solved; a novel electric energy router in an area is adopted for carrying out electric energy routing aiming at the current conversion links of the alternating current-direct current power distribution network with different voltage grades, the real-time information flow controls the power flow, and the method can be applied to the scene of the intelligent power distribution network to a certain extent.
The technical scheme of the invention is as follows: the method for calculating the power flow of the alternating-current and direct-current hybrid power distribution network is characterized by comprising the following steps of:
1) determining a topological structure of the whole power distribution network and determining a node type of the power distribution network;
2) constructing an alternating current-direct current hybrid power distribution network model taking a multi-port electric energy router as a core, and setting a series of parameters for the model;
3) setting loss parameters of the electric energy router;
4) carrying out load flow calculation based on a Newton method;
5) calculating to obtain the load flow of the whole alternating current-direct current power distribution network comprising the multi-port electric energy router, and simultaneously obtaining the voltage of each node;
6) and further, the line loss and the multi-port electric energy router loss can be obtained.
Specifically, the power flow calculation method is applied to a power distribution network in an area comprising a medium-voltage alternating-current power distribution network, a medium-voltage direct-current power distribution network, a low-voltage alternating-current power distribution network and a low-voltage direct-current power distribution network; and the medium and low voltage AC/DC distribution network performs electric energy routing through the multi-port electric energy router.
Specifically, the load flow calculation method is based on a Newton method, load flow calculation is performed on the low-voltage power distribution network firstly, electric energy output or injected from a port is obtained, and then load flow calculation is performed on the medium-voltage power distribution network.
Specifically, the load flow calculation method comprises the step of calculating the loss of a given multi-port electric energy router.
Further, the calculation of the loss of the given multi-port power router at least comprises VSC loss and DAB loss.
Specifically, the power flow calculation is performed according to the following steps:
1) inputting parameters of the whole power distribution network;
2) carrying out low-voltage alternating current network load flow calculation to obtain active power P1 and reactive power value Q1 flowing into VSC 1;
3) calculating an active power value P2 of the power value which flows through VSC1 and DAB1 and is injected into a medium-voltage direct-current bus;
4) carrying out load flow calculation on the low-voltage alternating-current power distribution network to obtain an active power value P3 injected into DAB 2;
5) calculating an active power value P4 injected into a medium-voltage direct-current bus after DAB 2;
6) carrying out load flow calculation on the medium-voltage direct-current power distribution network to obtain a power value P5 required by an internal direct-current bus;
7) active power P6 which is injected into the direct current bus through the medium-voltage alternating current port is P5-P4-P2; calculating the active power and the reactive power flowing through the VSC2 through P6;
8) and carrying out load flow calculation on the medium-voltage alternating-current power distribution network.
Specifically, the parameters of the whole power distribution network at least comprise new energy power generation parameters, node parameters and constraint limits.
Furthermore, the load flow calculation method is based on a Newton method, load flow calculation is firstly carried out on the low-voltage distribution network, and the nodes connected with the low-voltage alternating-current ports are controlled by adopting a fixed alternating-current voltage amplitude value and a fixed phase angle.
Furthermore, the load flow calculation method is based on a Newton method, load flow calculation is firstly carried out on the low-voltage distribution network, and nodes connected with the low-voltage direct-current ports are controlled by adopting fixed direct-current voltage.
Furthermore, the flow calculation method performs load flow calculation on the medium voltage distribution network after electric energy output or injected by the port is obtained, and controls the nodes connected with the medium voltage alternating current port by adopting constant reactive power and constant direct current voltage.
Compared with the prior art, the invention has the advantages that:
1. the technical scheme of the invention is mainly applied to the load flow calculation of the alternating current-direct current hybrid power distribution network in the area containing the new energy power generation device, and can effectively solve the problem that the traditional load flow calculation method cannot be applied to the novel alternating current-direct current hybrid power distribution network containing the new energy power generation equipment;
2. according to the technical scheme, a novel electric energy router in the region is adopted for carrying out electric energy routing aiming at the current conversion links of the alternating current-direct current power distribution network with different voltage grades, and the real-time information flow controls the power flow, so that the method can be applied to the scene of the intelligent power distribution network to a certain extent.
Drawings
FIG. 1 is a flow chart of a power flow calculation according to the present invention;
FIG. 2 is a schematic diagram of a regional distribution network model with an energy router applied in the present invention;
fig. 3 is a schematic view of a flow calculation process of the ac distribution network according to the present invention.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
The flow chart of the power flow calculation of the invention is shown in fig. 1.
Along with the development of a traditional power grid to a smart power grid, the controllability requirement on a power distribution network is gradually improved.
Compared with the traditional power distribution network, the alternating-current and direct-current hybrid power distribution network has the advantages that active power and reactive power can be adjusted more easily by using the flexible direct-current converter contained in the alternating-current and direct-current hybrid power distribution network, and the controllability of the alternating-current and direct-current hybrid power distribution network is compared with that of the traditional alternating-current power distribution network, so that the great.
The controllability is based on the fact that a power flow calculation result of the alternating current-direct current hybrid power distribution network is obtained firstly, and power flow control of the power distribution network is carried out according to the result.
Therefore, the purpose of the design of the alternating current-direct current hybrid power distribution network load flow calculation method in the technical scheme of the invention is mainly suitable for an intelligent regional power distribution network including the access of a new energy power generation device.
The main application scene of the invention is set as an alternating current and direct current hybrid power distribution network in an area with a multi-port electric energy router as a core, and the type of power distribution network mainly comprises a medium-voltage alternating current power distribution network, a medium-voltage direct current power distribution network, a low-voltage alternating current power distribution network and a low-voltage direct current power distribution network. The low-voltage alternating-current power distribution network and the low-voltage direct-current power distribution network are mainly responsible for accessing a new energy power generation device, such as photovoltaic power generation, wind power generation and the like. The medium-voltage direct-current power distribution network is mainly responsible for being interconnected with power distribution networks in other areas to transmit electric energy. The model of the AC/DC hybrid power distribution network is shown in FIG. 2.
1. The invention firstly needs to determine the node type of the power distribution network.
In the load flow calculation of the alternating-current distribution network, nodes can be divided into three types, namely PQ nodes, PV nodes and balance nodes. In a direct-current power distribution network, nodes can be divided into a fixed P node, a fixed I node and a fixed V node. In an alternating current-direct current hybrid power distribution network with a multi-port electric energy router, a medium-voltage alternating current power grid is regarded as a main grid and is mainly responsible for balancing power fluctuation of other sub-networks. In the load flow calculation of the direct current power distribution network, loads are classified according to the following conditions, and a P node is mainly a load directly connected to the direct current power distribution network; the fixed V node is mainly a node which needs the power electronic device to maintain constant voltage; and the I node is mainly an alternating current load which needs to be connected to a direct current distribution network through an inverter. The node type of the DC/DC converter depends on the control mode, and if constant voltage control is adopted, the node on the outlet side is a constant V node; if the voltage-regulating-free control is adopted, the node can be regarded as a fixed P node. For a power electronic converter connecting an alternating current power grid and a direct current power grid with a distributed energy source, if a node controlled by constant power is adopted, the node is specified as a constant P node, if a node controlled by constant voltage is adopted, the node is specified as a constant V node, and if a node controlled by constant current is adopted, the node is specified as a constant I node.
2. After the node type is determined, a basic principle flow of load flow calculation and constraint condition setting are given.
(1) Node power balance equation:
the node voltage equation of the power system:
node power balance equation:
simultaneous equations (1) and (2) may yield a general form of the power system flow equation:
substitution into
The rectangular coordinate power balance equation can be obtained:
(2) constraint conditions are as follows:
for an n-node system, 2n node equations can be written in a column, each node has 4 variables, namely active power P, reactive power Q, node voltage amplitude V and node voltage phase angle. PGi,QGiAre respectively a power supply sectionThe active power and reactive power values of the points. The constraints for the four variables are as follows:
Vmin,i≤Vi≤Vmax,ii＝1,2,…,n (6)
|i-j|≤|i-j|maxi,j＝1,2,…,n (7)
Pmin,Gi≤PGi≤Pmax,Gii＝1,2,…,n (8)
Qmin,Gi≤QGi≤Qmax,Gii＝1,2,…,n (9)
(3) and (3) calculating the load flow by a Newton method:
the technical scheme of the invention adopts a Newton method (Newton-Raphson method) to carry out load flow calculation, wherein the Newton method is an effective method for solving a linear equation and is also a most basic calculation method in the load flow calculation. For example, the currently used PQ decomposition method is simplified based on the Newton method. The theoretical basis of Newton's method is briefly described below using rectangular coordinates as an example.
For the non-linear equation f (x) 0, an initial value x is given(0)Expanded by Taylor series, the following expression is given:
ignoring the higher order terms, there are:
f(x(0))+f′(x(0))Δx(0)＝0 (11)
the flow of Newton method calculation load flow is as follows:
1) calculating the function value f (x)(k)) And judges whether or not to converge | | | f (x)(k))||≤；
2) Computing Jacobian matrices
3) Calculating correction amount
4) Correction of variables x(k+1)＝x(k)+Δx(k)And k is k + 1. Returning to the step 1); and if the convergence is achieved, outputting a calculation result.
(4) Port control mode setting:
because the novel alternating current-direct current hybrid power distribution network containing the multi-port electric energy router is greatly different from the traditional power distribution network, the diversity of ports and the diversity of control modes exist, and the control mode of the most common scene in the novel alternating current-direct current hybrid power distribution network is researched. Namely: for the VSC1 (located at the medium voltage ac port), constant dc voltage and constant reactive power control are adopted, and since the medium voltage dc node connected to the VSC1 is an internal dc bus and the voltage support is mainly by the medium voltage ac network, the VSC1 needs to adopt constant dc voltage control. Constant ac voltage magnitude and phase angle control is employed for the VSC2 (located at the low voltage ac port) because the ac nodes to which it is connected act as balancing nodes in the low voltage ac network. Constant dc voltage control is used for DAB1 (at the low voltage ac port) because it is connected to the dc side of VSC2, the dc voltage of which is determined by VSC 2. Constant dc voltage control is used for DAB2 (at the low voltage dc port), since it is responsible for maintaining the voltage of the low voltage dc distribution network, the dc node voltage connected to DAB2 should be constant.
(5) Aiming at the load flow calculation of an alternating current-direct current hybrid power distribution network in an area with a multi-port electric energy router as a core, the loss of the electric energy router is considered, and the loss mainly comprises VSC loss and DAB loss.
Firstly, obtaining a loss model of the VSC according to a comprehensive loss model of the power electronic transformer:
Ploss,vsc,i＝a2,iI2 i+a1,iIi+a0,i(13)
in the formula Ploss,vsc,iThe VSC device loss is designated i. Coefficient a0,i，a1,i，a2,iIs the loss factor of the VSC device numbered i and satisfies a0,i，a1,i，a2,iIs more than or equal to 0. Wherein a is0,iThe fixed loss is mainly the core loss of the high-frequency transformer, and is independent of the current flowing through the high-frequency transformer. a is1,iFor linear losses, mainly switching losses of switching devices (e.g., IGBTs) in the multi-port power router. a is2,iThe square loss is expressed, mainly the coil loss of a high-frequency transformer and the conduction loss of a middle switching device (IGBT) of the multi-port electric energy router. The VSC loss coefficients of different models are different, but most of the VSC loss coefficients can be expressed by the formula.
Aiming at DAB loss, because DAB develops rapidly, the loss is reduced along with the development, and the DAB loss of different models is greatly different, so that approximately 2% of the power flowing through the DAB loss is taken as the DAB loss. Therefore, the loss can be expressed by the following formula:
Ploss,DAB,i＝0.02×Pport,i(14)
example (b):
(1) as shown in fig. 2, an ac/dc hybrid power distribution network model with a multi-port electric energy router as a core is constructed:
a series of parameters are set for the model.
(2) Determining the node type contained in the model:
in a medium-voltage alternating-current power distribution network, a node connected with a high-power alternating-current power supply is taken as a balance node, and a node connected with a medium-voltage alternating-current port of a multi-port electric energy router is taken as a PQ node. In a low-voltage alternating-current power distribution network, nodes connected with new energy are divided into PQ nodes and PV nodes according to different types of the connected new energy, and the nodes connected with a low-voltage alternating-current port of a multi-port electric energy router are determined as balance nodes. In the low-voltage direct-current power distribution network, nodes connected with new energy are divided into a fixed P node and a fixed V node according to different types of the connected new energy, and nodes connected with low-voltage direct-current ports of the multi-port electric energy router are determined as balance nodes. In a medium-voltage direct-current power distribution network, an internal direct-current voltage bus is taken as a balance node, and load flow calculation is carried out.
(3) Setting loss parameters of the electric energy router:
from the two formulae mentioned above, a plurality can be obtainedLoss condition of each port of the port power router. First is the medium voltage ac port, a because it contains only VSCs and no DAB0,1Is equal to 0, and a2,iWithout copper loss of high-frequency transformer, its loss Ploss,1＝Ploss,vsc,1(ii) a The second is the low voltage ac port, which has a loss of P because it contains VSC and DAB modulesloss,2＝Ploss,vsc,2+Ploss.DAB,1. Finally, the low-voltage direct current port only comprises a DAB module, so the loss is Ploss,4＝Ploss.DBA,2. Because the medium voltage direct current port of the multi-port electric energy router does not contain any device and does not experience any conversion link, no loss can be considered.
(4) Using newton's method, the power flow calculation is performed as follows (see fig. 3).
1) And inputting parameters of the whole power distribution network, including new energy power generation parameters, node parameters, constraint limits and the like.
2) Performing low-voltage alternating current network load flow calculation to obtain active power P1 and reactive power value Q1 flowing into VSC1
3) Calculating the active power value P2 of the power value injected into the medium-voltage direct current bus through VSC1 and DAB1
4) Carrying out load flow calculation on the low-voltage alternating-current power distribution network to obtain an active power value P3 injected into DAB2
5) Calculating the active power value P4 injected into the medium-voltage direct-current bus through DAB2
6) Carrying out load flow calculation on the medium-voltage direct-current power distribution network to obtain a power value P5 required by the internal direct-current bus
7) The active power P6 injected into the dc bus through the medium voltage ac port is P5-P4-P2. Through P6, the active power and reactive power flowing through the VSC2 are calculated.
8) And carrying out load flow calculation on the medium-voltage alternating-current power distribution network.
Through the process steps, the load flow of the whole alternating current-direct current power distribution network comprising the multi-port electric energy router can be obtained through calculation, and the voltage of each node is obtained at the same time. And further, the line loss and the multi-port electric energy router loss can be obtained. The node voltage and the line of the power distribution network and the loss of the electric energy router are used as important evaluation criteria of the power grid condition in subsequent chapters.
In summary, the technical scheme of the invention mainly comprises the following steps of determining the topological structure of the whole power distribution network, performing node division on the power distribution network mainly aiming at the load flow calculation of the medium-low voltage alternating current and direct current power distribution network, determining the node type, and then performing four variables of each node: the method comprises the steps of determining constraint conditions of active power, reactive power, node voltage amplitude and node voltage phase angle, finally carrying out load flow calculation on a low-voltage distribution network on the basis of a Newton method according to a unified iteration method, obtaining electric energy injection data, then respectively carrying out load flow calculation on medium-voltage distribution networks, and finally obtaining load flow calculation results of the distribution networks in the whole area.
The innovation of the invention comprises two points:
1. the method is mainly applied to the load flow calculation of the alternating current-direct current hybrid power distribution network in the area containing the new energy power generation device, and can effectively solve the problem that the traditional load flow calculation method cannot be applied to the novel alternating current-direct current hybrid power distribution network containing the new energy power generation equipment;
2. the invention adopts a novel electric energy router in the region to carry out electric energy routing aiming at the current conversion links of the AC/DC power distribution network with different voltage grades, and controls the power flow by real-time information flow, thereby being applied to the scene of the intelligent power distribution network to a certain extent.
The technical scheme of the invention is applied to the load flow calculation of the alternating current and direct current hybrid power distribution network accessed by the new energy power generation device, and the regional power distribution network is a multi-voltage-level alternating current and direct current hybrid power distribution network connected by a multi-port electric energy router. The method mainly comprises the following steps of determining the topological structure of the whole power distribution network, performing node division on the power distribution network mainly aiming at the load flow calculation of a medium-low voltage alternating current-direct current power distribution network, determining the node type, and then performing four variables of each node: the method comprises the steps of determining constraint conditions of active power, reactive power, node voltage amplitude and node voltage phase angle, finally carrying out load flow calculation on a low-voltage distribution network on the basis of a Newton method according to a unified iteration method, obtaining electric energy injection data, then respectively carrying out load flow calculation on medium-voltage distribution networks, and finally obtaining load flow calculation results of the distribution networks in the whole area.
The method can be widely applied to the field of power flow calculation of power grid operation scheduling and alternating current-direct current hybrid power distribution networks.
Claims (10)
1. A load flow calculation method for an alternating current-direct current hybrid power distribution network is characterized by comprising the following steps:
1) determining a topological structure of the whole power distribution network and determining a node type of the power distribution network;
2) constructing an alternating current-direct current hybrid power distribution network model taking a multi-port electric energy router as a core, and setting a series of parameters for the model;
3) setting loss parameters of the electric energy router;
4) carrying out load flow calculation based on a Newton method;
5) calculating to obtain the load flow of the whole alternating current-direct current power distribution network comprising the multi-port electric energy router, and simultaneously obtaining the voltage of each node;
6) and further, the line loss and the multi-port electric energy router loss can be obtained.
2. The method for calculating the power flow of the alternating-current and direct-current hybrid power distribution network according to claim 1, wherein the power flow calculation method is applied to a power distribution network in an area comprising a medium-voltage alternating-current power distribution network, a medium-voltage direct-current power distribution network, a low-voltage alternating-current power distribution network and a low-voltage direct-current power distribution network; and the medium and low voltage AC/DC distribution network performs electric energy routing through the multi-port electric energy router.
3. The method for calculating the power flow of the alternating-current and direct-current hybrid power distribution network according to claim 1, wherein the method for calculating the power flow is based on a Newton method, the power flow calculation is performed on a low-voltage power distribution network firstly, electric energy output or injected from a port is obtained, and then the power flow calculation is performed on a medium-voltage power distribution network.
4. The method of claim 1, wherein the method comprises calculating the loss of a given multiport power router.
5. The method for calculating the power flow of the AC/DC hybrid power distribution network according to claim 4, wherein the calculation of the given multiport electric energy router loss at least comprises VSC loss and DAB loss.
6. The method for calculating the power flow of the alternating current-direct current hybrid power distribution network according to claim 1, wherein the power flow calculation is performed according to the following steps:
1) inputting parameters of the whole power distribution network;
2) carrying out low-voltage alternating current network load flow calculation to obtain active power P1 and reactive power value Q1 flowing into VSC 1;
3) calculating an active power value P2 of the power value which flows through VSC1 and DAB1 and is injected into a medium-voltage direct-current bus;
4) carrying out load flow calculation on the low-voltage alternating-current power distribution network to obtain an active power value P3 injected into DAB 2;
5) calculating an active power value P4 injected into a medium-voltage direct-current bus after DAB 2;
6) carrying out load flow calculation on the medium-voltage direct-current power distribution network to obtain a power value P5 required by an internal direct-current bus;
7) active power P6 which is injected into the direct current bus through the medium-voltage alternating current port is P5-P4-P2; calculating the active power and the reactive power flowing through the VSC2 through P6;
8) and carrying out load flow calculation on the medium-voltage alternating-current power distribution network.
7. The method for calculating the power flow of the alternating current-direct current hybrid power distribution network according to claim 6, wherein the parameters of the whole power distribution network at least comprise new energy power generation parameters, node parameters and constraint limits.
8. The method for calculating the power flow of the alternating-current and direct-current hybrid power distribution network according to claim 1, wherein the power flow calculation method is based on a Newton method, power flow calculation is firstly carried out on the low-voltage power distribution network, and a node connected with a low-voltage alternating-current port is controlled by using a constant alternating-current voltage amplitude value and a constant alternating-current voltage phase angle.
9. The method for calculating the power flow of the alternating-current and direct-current hybrid power distribution network according to claim 1, wherein the power flow calculation method is based on a Newton method, power flow calculation is firstly carried out on the low-voltage power distribution network, and nodes connected with low-voltage direct-current ports are controlled by constant direct-current voltage.
10. The method for calculating the power flow of the alternating-current and direct-current hybrid power distribution network according to claim 1, wherein the flow calculation method is used for carrying out power flow calculation on the medium-voltage distribution network after electric energy output or injected from a port is obtained, and constant reactive power and constant direct-current voltage are adopted for a node connected with a medium-voltage alternating-current port.
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