132 results about "Active power flow" patented technology

The invention relates to a symmetry method for obtaining multitermianl direct current power network nonlinear active power flow. First a symmetric nonlinear indeterminate equation system (S1) of node injected active power with respect to node voltage offset is buit, then a symmetric linear linear indeterminate equation system (S2) of a node injected active power increment with respect to a node voltage offset increment is built according to the symmetric nonlinear indeterminate equation system, node voltage offset of each node and the total quantity of node voltage (S3) in the multiterminal durect current power network are obtained according to the symmetric linear indeterminate equation system and known node injected active power, and finally nonlinear active power flow (S4) of each branch in the multiterminal durect current power network is obtained according to the node voltage offset of each node in the multierminal direct current power network, whrein the node voltage offset of all nodes in the multiterminal direct current power network is equally treated, the obtained all node voltage offset always draws close to zero, a reference node does not need to be selected, and obtained nonlinear active power flow is uniqud and reasonable.

The invention discloses an active power flow optimizing distribution method for an alternating-direct current parallel system containing soft direct current power transmission, and solves the reasonable distribution problem of the active power flow of the alternating-direct current system under the alternating-direct current parallel operation mode of the soft direct current power transmission. The method comprises the steps of obtaining basic parameters of a power grid to be analyzed; establishing corresponding target functions by taking factors such as alternating-direct current equipment loss, avoiding parallel loop current, the safety and stabilization of the power grid, the utilization rate of the alternating-direct current equipment and fault rate as target conditions according to the obtained basic parameters of the power grid; establishing multiple target optimization functions according to all established target functions; designing a subjection function for each target function according to the fuzzy theory; and resolving the optimal solution of the multiple target functions by adopting a fuzzy algorithm. The method considers the constrain of multiple target conditions, obtains the optimal active power control reference value under the alternating-direct current parallel operation of the soft direct current power transmission system by resolving the multi-target optimal function, and is more reasonable in comparison with the method relying on experience to set the active power reference value.

The invention provides a power system cascading failure simulation method based on a unified power flow controller and belongs to the technical field of power system security and reliability protection. A computer is used for determining the installation position of the unified power flow controller in a power system firstly, determining an active power flow betweenness threshold value of each node of the power system, performing power system cascading failure simulation based on the unified power flow controller and finally calculating measurement index for reflecting severity of cascading failure through procedures. The power system cascading failure simulation method gives consideration to power flow directivity and the operation mode of the system, optimizes the installation position for installing the unified power flow controller, effectively performs line parameter regulation while meeting safe operation constraints of the power system, and can reflect the propagation process of the cascading failure of the power system actually. The power system cascading failure simulation method based on the unified power flow controller can be widely applied to the cascading failure simulation of the power system, is particularly suitable for the cascading failure simulation of a large-scale complicated power system, and provides a scientific basis for preventing occurrence of the cascading failure of the power system.

The invention discloses a two-stage initiative separation method based on normalized spectral clustering and constrained spectral clustering. The method comprises the steps of: in the first stage, recognizing coherent generator groups by using normalized spectral clustering and forming pairwise constraints by using the coherent generator groups; and in the second stage, finding separation sections satisfying the pairwise constraints and with the minimum active power flow shock by using constrained spectral clustering. When a system needs to be separated into a plurality of islands, a recursive bisection method can be adopted. The algorithm provided by the invention takes two factors, i.e., generator coherency and the minimum active power flow shock, into account, and the initiative separation problem can be calculated in real time without simplifying system topology.

The invention discloses a flexible looped network control system operation and power flow optimization method, and belongs to the field of electric power system operation and power flow optimization. The method solves the problem of reasonable system active power flow allocation problem under the normal and fault conditions of the flexible looped network control system. The method includes the steps that network parameters of a target power grid are obtained in real time based on a D5000 system; according to the obtained power grid basic parameters, the element load rate and the system power supply capacity serve as target conditions, and corresponding target functions are built; a multi-target optimization function is determined based on all the target functions; according to a fuzzy theory, subordinating degree functions of all the target functions are made, and the optical solution of the multi-target optimization function is obtained through a fuzzy algorithm. According to the method, the multiple target functions serve as constraint conditions, the optimal power flow allocation under the normal and fault operation conditions of the flexible looped network control system is obtained, and the reliability and economy of power grid operation are improved.

The invention discloses an electric system active power real-time dispatching method considering wind power prediction error. The electric system active power real-time dispatching method comprises the following steps of describing random distribution character of the wind power prediction error by using Laplace distribution; by taking economic efficiency optimum and wind curtailment minimum as two targets, introducing a chance constraint condition; solving active power flow probability distribution of a system on the basis of a probabilistic power flow method for Latin hypercube sampling; establishing a buffer generator set active power optimum allocation model considering the wind power prediction error, and solving a chance constraint planning model by adopting an improved genetic algorithm. According to the electric system active power real-time dispatching method disclosed by the invention, the wind power prediction error is considered during real-time dispatching, power unbalance and flow off-limit brought to the system by wind power output offset can be avoided, and the safe operation of the system is guaranteed; moreover, while the wind power prediction error is assimilated, the wind power accepting ability is increased by the system.

The present invention proposes a power grid node importance degree determination method. The power grid node importance degree determination method comprises: firstly, abstracting a power grid into a directed graph according to a topological connection condition and an active power flow direction; secondly, in order to combine node importance degree evaluation with an operating mode of the power grid, taking power supply and load apparent power of a node as a branch flowing in and out of the node by introducing a power supply node and a load node, and using a value of power flow apparent power of the branch as a weight of the directed graph; and and thirdly, in combination with the actual circumstance of the power grid, defining a measurement index of a power grid node importance degree to be the sum of an authority value and a hub value of the node, and adopting an MBCC-HITS algorithm to implement the calculation of the power grid node importance degree. The power grid node importance degree determination method provided by the present invention can reasonably and efficiently calculate importance degrees of nodes of the power grid. The result is closely related to the operating mode. The node importance degrees obtained with the method can be applied to the aspects of risk evaluation, maintenance schedule optimization arrangement and the like of power grids at different levels.

The invention discloses a power grid component cascading failure simulation method. According to the invention, voltage and line active power flow, which have great influences for the failure rate of a component, are selected to act as variables to correct the failure rate of the component so as to enable the simulation to be closer to the reality; traditional methods such as proportional load shedding, nearby load shedding and load shedding performed according to the importance degree of loads are abandoned when load shedding is performed, an optimal load shedding method is adopted, and all factors, which can be used for adjustment, in the system are comprehensively utilized, so that a problem of load shedding is well solved theoretically so as to acquire an operation scheme capable of enabling the overall benefit of the system to be the highest; and the power grid component cascading failure simulation method not only considers an alternating-current mode, but also considers a direct-current mode in power flow calculation, so that both the calculation accuracy and the calculation speed are well considered.

The invention discloses an electrified railway in-phase power supply and transformation system, which relates to the technical field of AC electrified railway power supply. The in-phase power supply and transformation system comprises n traction substations, a single-phase high-voltage transmission line and a traction network, wherein, the first traction substation comprises a three-phase high-voltage bus bar, a first main transformer connected with the three-phase high-voltage bus bar and a negative sequence compensation device connected with the three-phase high-voltage bus bar; The second traction substation to the nth traction substation are respectively connected with the single-phase high-voltage transmission line and the traction network. The negative sequence compensation device isinstalled in the first traction substation, and comprises a three-phase compensation transformer, a three-phase reactive power compensation device and a measurement and control unit. The negative sequence compensation device generates the negative sequence power flow through the three-phase reactive power compensation device, and does not change the active power flow of the whole system; At the same time, the power supply mileage of electrified railway without phase separation is greatly prolonged by using the advantages of large transmission power and long transmission distance of high voltage transmission line.

The invention discloses a method for realizing ice melting in a distribution network by making an active ring current with flexible multi-state switches. The method comprises: selecting an ice-meltingtarget line; reconstructing a distribution network through a distribution network communication switch and reconstructing the ice-melting target line into an ice-melting ring network path; setting working modes of flexible multi-state switches; to be specific, setting a flexible multi-state switch at the ice-melting target line side to work in a PQ mode and a flexible multi-state switch at a non-ice-melting communication line side to work in a direct-current constant-voltage control mode; and calculating an active power P of the ice-melting line based on an ice-melting current needed by the ice-melting target line, using the P as an active power reference value of the flexible multi-state switch at the side, starting the flexible multi-state switches at the two sides, and adjusting voltage phases of the flexible multi-state switches, and generating an active power flow in positive correlation with a phase difference value. Therefore, problems of complicated line outage operation and the short-circuiting procedures melting efficiency and the limited length of the ice-melting line during the ice melting of the transmission line in the prior art can be solved.

The invention discloses a security constrained optimal power flow method based on power flow transfer relation. The method is characterized by establishing active power flow transfer relationship before and after fault based on anticipated fault analysis; describing fault-state branch active power flow into a ground-state branch active power flow function, so that the fault-state branch active power flow constraint is described as ground-state branch active power flow linear inequality constraint; and carrying out grouping on parallel circuits and parallel main transformers, and reducing the scale of monitored branches by utilizing power flow distribution relationship of branches in each group, and carrying out filtering on the fault-state branch active power flow constraint by utilizing the characteristic that short-time flow capacity of a device is obviously larger than long-term flow capacity thereof to minimize the calculation scale of the SCOPF problem as far as possible. The method has a good effect.

The invention relates to a DC power flow calculation method considering charging capacitance. The DC power flow calculation method comprises steps of (1) calculating a trigonometric function simplification method and an approximation coefficient, (2) constructing a DC power flow model considering a charging capacitance, (3) incorporating a circuit model containing a charging capacitor and a grounding admittance, (4) using a complete admittance matrix parameter to calculate a coefficient matrix, (5) solving voltage amplitudes of all PQ nodes through back substitution of a correction phase angle to obtain voltage amplitudes and phase angles of all nodes in a network and using complex power flow equation to calculate line circuit complex power. Compared with a DC power flow algorithm without considering a charging capacitance, the DC power flow calculation method improves calculation accuracy of the voltage amplitude and the reactive power flow on the premise that the active power flow calculation accuracy of the current DC power flow algorithm is maintained, and enables the power flow algorithm to be adapted to calculation of reactive power flow of a power transmission system.

The invention discloses an adaptive precise harmonic compensation method based on a photovoltaic grid-connected system. The method comprises the following steps: detecting output current and an outputvoltage on an AC side of a photovoltaic grid-connected inverter when the photovoltaic grid-connected inverter works at a maximum power tracking point; detecting the remaining capacity of the photovoltaic grid-connected inverter, judging the active power flow directions of different subharmonics, and formulating a compensation strategy; adaptively outputting a to-be-compensated component switch on-off signal according to the remaining capacity of the photovoltaic grid-connected inverter; and achieving precise harmonic compensation by using a repeated double closed-loop controller according tothe switch on-off signal. According to the adaptive precise harmonic compensation method disclosed by the invention, the remaining capacity of the inverter is dynamically tracked according to the external illumination changes, the compensation cost of the photovoltaic inverter can be effectively reduced, and the distortion rate of the grid side harmonics is maximally reduced while making full useof the limited remaining capacity of the photovoltaic grid-connected inverter.

The invention discloses a negative sequence compensation device and method of an electrified railway in-phase power supply and transformation system, belonging to the technical field of electrified railway power supply. The in-phase power supply substation system comprises a first traction substation, a second traction substation,... and an n-th traction substation, n >= 2; The first traction substation, the second traction substation,... and the nth traction substation are respectively connected with the single-phase high-voltage transmission line and the traction network; The negative sequence compensation device is installed in the first traction substation and comprises a three-phase compensation transformer, a three-phase reactive power compensator connected with the three-phase compensation transformer and a measurement and control unit connected with the three-phase reactive power compensator. The invention can effectively solve the technical problem that the active power flow of the traction substation group is not changed, and the negative sequence centralized compensation of the traction substation group is solved through the reactive power flow control.

The invention discloses a timing sequence optimization control method for a distributed power flow controller, and the controller, wherein a DPFC (deviation of power frequency component) device is connected into a single-machine infinite bus system, and the both ends of the single-machine infinite bus system are connected with a Y-Delta-type transformer; the DPFC device is used for switching current converters at the series side of the DPFC device in different time periods, and the number of the current converters switched in each time period is calculated according to a corresponding formula. According to the timing sequence optimization control method disclosed by the invention, the active power flow of an electric transmission line is adjusted in real time by controlling the switching time of the single-phase current converters at the series side of the DPFC device; simultaneously, the reduction of the active power of the electric transmission line during the charging energy storage process of direct-current capacitors at the series side of the DPFC device is prevented, the total harmonic distortion of a line current caused by the plurality of single-phase current converters is avoided, and the reactive compensation performance of the DPFC device is optimized.

The invention provides an AC-DC power grid vulnerable line analysis method. The method comprises the steps of acquiring a topological structure of an AC-DC power grid to calculate an original active power flow of each line in the AC-DC power grid, determining and simulating the active power of each line after each line is cut off, calculating an active power flow increment matrix in combination with the original active power of each line, and further acquiring an AC power flow transfer correlation matrix in combination with the safety margin of each line, calculating AC line power flow increment caused by DC locking and influence indexes of AC line on-off on a DC system, and acquiring an AC-DC power flow transfer correlation matrix in combination with the AC power flow transfer correlationmatrix, and converting the AC-DC power flow transfer correlation matrix into a line vulnerability degree vector to obtain a line with the highest vulnerability value as a power grid power failure keyline. By implementing the method, the mutual influence between the AC system and the DC system is considered, and the key line which has an important influence on the cascading failure of the power system can be identified, so that the analysis on the vulnerable line of the AC and DC power grid is realized.

The invention discloses a method for calculating the active power of a stable section after an ultra-high voltage direct current blocking fault. According to the active power imbalance caused by the direct current blocking fault, the method distributes the active power imbalance amount to each generator according to a synchronous power coefficient, and calculates the active power flow of the section at the fault instant. Aiming at the unbalance of active power caused by DC blocking fault and safety control system operation, the active power of generator and load node is determined according tothe static frequency characteristic, and the section active power flow from transient state to steady state is calculated. The active power of generator and load node is determined according to the spinning reserve and climbing rate of generator in the process of recovering to the rated frequency, and the section active power flow in the process of secondary frequency modulation is calculated. The invention respectively calculates the section active power flow in the instant of fault, the transient process transitioning to the steady state and the secondary frequency modulation operation process according to the DC blocking fault, and realizes the fast analysis of the stable section active power under the large-scale active power unbalance quantity.

The invention discloses a power distribution transformer power supply area interconnection-based power distribution network management and control method. The method comprises the following steps that: the data of each transformer power supply area of a power distribution network are collected, and the working state of each transformer power supply area is analyzed; in response to the low-load operation of the plurality of transformer power supply areas, a load concentration instruction is sent out, so that the load of the low-load transformer power supply areas is interconnected to other non-low-load transformer power supply areas; in response to the alternating current interconnection of the transformer power supply areas and the overload operation of a certain transformer power supply area, a load dispersion instruction is sent to disperse the load of the overload transformer power supply area to a non-overload transformer power supply area; and in response to the direct current interconnection of the transformer power supply areas and the overload operation of a certain transformer power supply area, a load support instruction is sent to transmit active power flow to the PCS ofthe overload transformer power supply area, or a power constraint instruction is sent to limit the active power flow of the PCS of the overload transformer power supply area. The invention further discloses a corresponding system. According to the method of the invention, load concentration is realized, so that low-load distribution transformers are relieved; load dispersion, load support or power constraint are realized, so that overload distribution transformers are adjusted, and the operation benefits of a power grid are effectively improved.

The invention provides a negative sequence compensation control device, system and method of a traction substation group. The negative sequence compensation control device comprises n current transformers and n voltage transformers of n traction substations in the traction substation group, a fiber network and a controller, wherein an input end of the controller is connected with a first current transformer and a first voltage transformer of a first traction substation and then is connected with the current transformers and the voltage transformers of other (n-1) traction substations by the fiber network, and an output end of the controller is connected with a control end of a three-phase passive power compensation device. By the negative sequence compensation control device, the equipmentproblem of concentrated compensation of dispersed negative sequences generated by each traction substrate and the technical problem of real-time compensation can be effectively solved without changing active power flow of a traction network of the traction substation group.

The invention relates to a UPFC line side reactive power flow optimization control method. The core idea is that reactive power consumed by lines is provided by a UPFC, and the sending end and receiving end power grids do not provide reactive power. The method comprises the following steps: calculating the reactive power loss of a line according to the current effective value of the line and the power grid impedance, and taking the reactive power loss as a line reactive power flow instruction of a series side converter of a UPFC; and performing subtraction between the reactive power of a sending end power grid and zero, and carrying out closed-loop control to get a reactive power instruction of a parallel side converter. Through the method, the capability of the UPFC to control the active power flow of lines is enhanced under constant capacity of the UPFC. Moreover, as the UPFC provides reactive power for lines, the influence of the reactive power loss of lines to the power grid voltage is reduced, and the stability of the sending end and receiving end power grids is improved.

Disclosed is a single-phase and three-phase conversion system based on MMC units. Each MMC unit is formed by connecting 10 bridge arms, wherein four bridge arms constitute a single-phase inverter and form a single-phase alternating-current port, and the other six bridge arms constitute a three-phase inverter and form a three-phase alternating-current port. Each MMC bridge arm is formed by connecting p structurally-identical power modules and an MMC bridge arm inductor L in series. The power modules are of a single-phase half bridge structure and are respectively composed of an IGBT half bridge and a direct-current energy storage capacitor. The single-phase alternating-current ports of n MMC units are connected in series with a high-voltage system. The three-phase alternating-current ports of the MMC units are insulated from each other and are independently connected with a low-voltage system. Two-way active power flow between the single-phase high-voltage system and the three-phase low-voltage system is realized. A matching transformer is omitted, which enables the system to have the advantages of small size, light weight, high efficiency, and less investment. The single-phase and three-phase conversion system based on MMC units is advanced and reliable in technology, and is easy to implement.