232 results about "Active power control" patented technology

The invention discloses a system and a method for analyzing stability and oscillation transmission of a network-forming converter system, and belongs to the technical field of virtual synchronous generator control, and the system comprises an active power control loop which takes an active power deviation value as input, and outputs a power angle of a VSG system through an active integration part and a feedback part; the reactive power control loop takes the reactive power deviation ratio as input, and outputs the voltage amplitude of the VSG system through an active integration part and a feedback part; according to the analysis method, whether each state variable is stable or not is judged firstly, and then the intensity of oscillation transmission between the state variables is judged. According to the method, the stability of the system can be evaluated more accurately, and the accuracy of system stability analysis under dynamic disturbance is ensured; an oscillation transfer effect function is introduced, and the mutual influence between different state variables is quantitatively analyzed; and the dynamic fluctuation range of each state variable in the system can be accurately evaluated.

The present invention belongs to the technical field of wind farm active power control and discloses a wind farm frequency modulation power distribution method that takes into account the historical fatigue load of the unit. The method comprises the following steps: collecting the frequency data of the wind farm grid connection point; when the frequency change exceeds the frequency modulation dead zone, calculating the wind farm active power change reference value ΔP farm ; Match the station active power change reference value ΔP in the formed scenario strategy set farm The corresponding optimized active power distribution results of the units. This distribution method is compared with the traditional proportional distribution scheme. While meeting the system frequency response requirements, the present invention improves the problems of sudden increase in fatigue load in wind farms and large differences in fatigue accumulation between units, and verifies the effectiveness of the proposed method.

The invention discloses a photovoltaic power station multi-source inverter active power control method and system, and relates to the technical field of photovoltaic power station active power control, and the method comprises the steps: calculating the dynamic performance score of each inverter based on the response time, conversion efficiency and health degree data of a multi-source inverter of a target photovoltaic power station; dividing the multi-source inverter into a response group and a steady-state compensation group based on the dynamic performance score and the dynamic division threshold; based on a preset allocation proportion, allocating the scheduling power regulation quantity to the response group and the steady-state compensation group; monitoring the overall output power of the target photovoltaic power station in real time; if the overall output power does not reach the target power range within the preset time, the active power output proportion of the response group is adjusted based on the prediction model; and after the overall output power of the target photovoltaic power station reaches the target power range, starting steady-state power replacement. The technical problem that the prior art cannot adapt to real-time working condition changes is relieved.

The invention provides a wind-light-heat-storage large-scale new energy base frequency coordination control method, and belongs to the field of power system active power control, and the method comprises the steps: carrying out the simulation analysis based on a wind-light-heat-storage large-scale new energy base DC sending-out system through a photo-thermal power generation system dynamic model, and obtaining a wind-light-heat-storage large-scale new energy base frequency coordination control model; analyzing the frequency modulation energy of the network-following type energy storage and the network-constructing type energy storage, constructing a wind-light-heat storage frequency response model, performing difference analysis on the response speed, and performing off-line solution to obtain a frequency response characteristic table; frequency modulation resources under different operation conditions are researched, and a coordinated output relation is obtained; deviation calculation is carried out to obtain a real-time deviation result, strategy matching is carried out by utilizing a frequency response characteristic table, a frequency modulation strategy is obtained and optimized in combination with a coordinated output relation, and a completely distributed frequency control strategy is obtained; according to the invention, reliable interaction of heterogeneous resource operation states in the primary frequency modulation scale and reasonable distribution of power output are realized.

The invention relates to a wind turbine generator active power control method and system based on the lowest inertia demand of a power system, and belongs to the technical field of wind turbine generator power control methods. The method comprises the following steps: (1) estimating the minimum inertia demand of the power system under the transient frequency security constraint of the system; (2) hierarchical adaptive virtual inertia control strategies including wind power plant virtual inertia demand calculation, a wind power plant virtual inertia hierarchical control strategy and a single machine virtual inertia control strategy; and (3) applying the strategy in the step (2) to power system control. Coordinated frequency modulation among the wind power station, the traditional thermal power plant and multiple machines in the wind power station is realized, and the problem of secondary frequency disturbance caused by group modulation and group control rolling optimization and frequency modulation quitting is solved.

The invention discloses a safety control method and system for an emerging control main body, and belongs to the technical field of power system active control, and the method comprises the steps: carrying out the bidirectional data interaction through a master station AGC and a field station AGC, and carrying out the bidirectional data interaction based on a bidirectional data interaction result and a cooperative anti-error parameter; whether the emerging control main body is in a controllable state or not is judged in real time through collaborative security locking logic; if the control main body is in the controllable state, active measurement data of the emerging control main body are obtained, and jump detection and multi-source checking are carried out on the active measurement data; after verification is passed, a pre-control instruction is generated based on the control strategy, and reasonability verification and control effect simulation verification are carried out; and after the control effect simulation verification is passed, the pre-control instruction is taken as a final control instruction to be issued to the emerging control main body for execution. The method can greatly improve the safety control capability of AGC on an emerging control main body, guarantees the frequency operation safety of a power grid, and improves the safe and reliable power supply capability of the power grid.

Disclosed in the present invention are a control method and system capable of providing frequency support for a flexible interconnected power distribution network. The method comprises: using a permanent-magnet direct-drive wind turbine connected to a flexible interconnected power distribution network to provide frequency support, measuring a direct-current voltage of a grid-side converter of the wind turbine, calculating a per-unit value and the phase of the direct-current voltage, and calculating the amplitude of a modulation voltage; generating a trigger pulse signal; monitoring the rotation speed of a wind turbine rotor and the rotor position angle of a synchronous generator, and acquiring a per-unit value of optimal power; calculating an active power reference value; on the basis of active power control and current control, outputting a d-axis component and a q-axis component of a modulation voltage of a generator-side converter, and by means of rotating coordinate transformation, generating a three-phase modulation voltage in a stationary coordinate system; and generating a trigger pulse signal by means of a pulse width modulation stage. The present invention enables wind turbines to provide quick response for power distribution networks in a frequency support stage, and prevent rotation speed stalling and suppress secondary frequency drop in a rotation speed recovery stage, thereby improving the support capability of the wind turbines for power grids.

The invention discloses a method for improving stability of a network-forming converter by considering voltage and phase transients, which solves the problem of over-current control blind areas existing at the initial stage of a fault and at the moment of clearing in a traditional single current limiting method and overcomes the defect that the stability is sharply deteriorated when a traditional strategy is used for coping with a composite fault. The method comprises the following steps: S1, obtaining a virtual synchronous machine swing equation under a synchronous rotating coordinate system and an equivalent circuit model under the action of a circular current limiter; and S2, obtaining a nonlinear relation between the output power and the power angle of the converter, and analyzing a transient stability domain of the converter during a fault period. And S3, obtaining a mixed current limiting strategy, deducing an equivalent circuit model corresponding to the strategy, and further obtaining an output power expression corresponding to the strategy. And S4, obtaining a power damping term acting on an active power control loop, further obtaining a synchronization stability improvement strategy, and deducing a closed-loop model describing the system at the moment.

The invention provides a VSG transient support capability improvement strategy based on active deviation integral feedback. The strategy comprises the following steps: constructing a VSG active control loop based on active power deviation integral feedback; based on the VSG active control loop, calculating an integral feedback compensation value based on power deviation control; and based on the integral feedback compensation value, the limit fault clearing time is prolonged. According to the strategy provided by the invention, the power angle change rate of the VSG can be effectively inhibited in the fault process, the limit fault clearing time is prolonged, and the transient power angle stability is improved.

The invention discloses a distributed new energy active power regulation and control method, device and equipment and a storage medium, and is used for solving the technical problems that an existing distributed new energy regulation and control mode is low in accuracy and poor in self-adaptability and real-time performance. Comprising the following steps: calculating a distribution network voltage compensation vector by adopting voltage deviation values of all distribution network nodes and an inverse matrix of a voltage sensitivity matrix; equally dividing the whole network power regulation quantity according to the number of the distributed energy equipment accessed to the distribution network node to generate a main network demand regulation vector; performing weighted fusion on the main network demand adjustment vector and the distribution network voltage compensation vector to obtain a global active adjustment target vector; calculating an equipment adaptation index of the distributed energy equipment by adopting an equipment adjustment capability parameter of the distributed energy equipment, a dominant frequency component in a global active adjustment target vector, a main network real-time power margin and a voltage deviation value; and allocating the adjustment task in the global active adjustment target vector to the distributed energy equipment for execution by adopting the dominant frequency component and the equipment adaptation index.

The invention relates to the technical field of new energy station power control, and discloses a wind and light storage active power control method and system based on a whale optimization algorithm, and the method comprises the steps: obtaining the equipment parameters of all wind and light storage equipment, and generating the dynamic priority of all equipment in combination with the real-time operation state; the initial whale population is generated as a plurality of power distribution schemes, each whale represents a group of power distribution coefficients, and the sum of the distribution coefficients is 1; constructing a fitness function for calculating a fitness value based on a weighted error term determined by a dynamic priority and a device and system dual penalty term; executing a main optimization loop, dynamically adjusting a search strategy through a convergence factor, updating the whale position by combining a bubble attack strategy and a surrounding strategy, generating a distribution scheme meeting a preset constraint condition, normalizing the optimal whale position, and outputting a power distribution coefficient of each device; and according to the distribution coefficient and the total power instruction, generating a specific power instruction value of each device for controlling the active power of each device, so that dynamic adjustment can be performed in real time according to the operation state of the device and the demand of the system, stable operation of the system and effective output of energy are ensured, and economic benefits are improved.

The invention discloses a time sequence fault current-limiting control method and system compatible with a grid-connected guide rule for a network construction type doubly-fed wind turbine generator, and the method comprises the following steps: freezing external power control when a low-voltage ride-through event of a power grid is detected at the initial stage of a fault, and suppressing transient overcurrent through dynamically adjusting the resistance component of virtual impedance; in the fault stable stage, an electromotive force compensation increment is calculated on the basis of grid-connected guide rule requirements at the moment 4 tau after the fault occurs; in the fault clearing stage, after it is detected that the fault is cleared, electromotive force compensation is stopped; gradually recovering the virtual impedance to a rated value through the dynamic coefficient A; in the fault recovery stage, active control and reactive control are recovered in sequence, power output is recovered to the level before the fault within one second, and meanwhile the virtual impedance amplitude is gradually recovered to the rated value along with the voltage phase difference; the voltage phase jump amplitude and the voltage drop amplitude determined by the method have high robustness.

The invention relates to a virtual inertia-damping cooperative adaptive control method for a voltage source type direct-driven permanent magnet wind turbine generator. The method comprises the following steps: constructing a voltage source type direct-driven permanent magnet wind turbine grid-connected equivalent model; constructing a wind turbine generator frequency response model based on a dynamic coupling relationship between virtual inertia and virtual damping; collecting a frequency signal of a common connection point of a power grid, and carrying out collaborative optimization processing on the frequency signal by adopting a composite filter to obtain a virtual power increment; the active power reference value is introduced into an active power control loop of the grid-side converter; and controlling the power grid side converter after the additional power reference value is introduced by adopting a rotational inertia and damping coefficient adaptive control method based on a nonlinear function. According to the method, frequency steady-state deviation compensation and dynamic change rate correction can be realized, the frequency stability under wide-range disturbance can be improved through segmented nonlinear adjustment, and the requirements of unit active inertia response and power grid frequency stability are met.

The present invention discloses a method for self-clearing DC faults in a new energy island power grid transmission system. The sending end adopts a constant AC voltage and frequency control strategy, and there is only one receiving end that adopts a constant DC voltage control strategy, while the remaining receiving ends adopt a constant active power control strategy. At the same time, each pole of the flexible DC converter station at the sending end real-time detects the DC current flowing out of this pole, and each pole of the flexible DC converter station at the receiving end real-time detects the DC current flowing into this pole. After detecting the occurrence of a DC fault, the DC fault is automatically cleared according to their respective control strategies, and the energy balance of the sending end island is achieved in cooperation with the AC energy consumption at the sending end. It solves the technical problems of coordinated control between flexible DC and new energy, power surplus, and self-clearing of DC faults on the DC side, and improves the power regulation ability and system stability of the new energy island power grid transmission system.

The invention belongs to the technical field of power grid control, and relates to a transformer area flexible interconnection system three-phase imbalance control method and device and a medium. Taking the transformer area converter controlled by the PQ control algorithm as a target transformer area converter; collecting a first control parameter output by an active power PI controller of the target transformer area converter; based on the upper and lower limits of the voltage target value of the DC bus, performing amplitude limiting setting on the first control parameter of the target transformer area converter to obtain the voltage target value; subtracting the voltage target value from the actual voltage value of the direct-current bus, inputting the difference value into the PI controller, and outputting a second control parameter of the target transformer area converter; taking the second control parameter as a direct-axis current target value, subtracting the direct-axis current target value from a direct-axis current actual value, and taking the difference value as the input of a direct-axis current PI controller; and controlling the target transformer area converter based on the voltage modulation signal output by the PQ control framework. The scheme can effectively improve the power supply reliability of the power distribution area and stabilize the DC bus voltage.

The invention relates to the technical field of power systems, and discloses an active control method and related equipment for a distributed new energy station, and the method comprises the steps: receiving an active adjustment instruction issued by a main station through an edge gateway, verifying the active adjustment, and generating verified instruction data; dynamically selecting a control mode based on the verified instruction data and the real-time operation state of the new energy station, and adjusting the active power output of the power generation equipment according to the control mode; and triggering a corresponding safety protection strategy after detecting that the power grid operates abnormally so as to isolate the abnormities according to the safety protection strategy and maintain stable operation of the power grid. Accuracy, timeliness, flexibility and safety of active control of the distributed new energy station can be improved, stable operation in a complex and changeable power grid environment can be ensured, and stability and reliability of power grid operation are improved.

The invention relates to the technical field of offshore wind power grid connection, in particular to a low-frequency oscillation suppression method for an offshore wind power synchronous machine grid connection system, which comprises the following steps: acquiring inherent parameters of the synchronous machine grid connection system and active power reference instructions of each fan of an offshore wind power plant; according to the inherent parameters, control parameters of a preset damping controller are determined, and the damping controller is configured based on the control parameters; acquiring an actual operation frequency signal of the offshore low-frequency power grid in real time, and comparing the actual operation frequency signal with a preset rated frequency of the offshore low-frequency power grid to obtain a frequency deviation signal; inputting the frequency deviation signal into a configured damping controller, and outputting a damping power instruction; and superposing the damping power instruction and the active power reference instruction to generate an active power control instruction. According to the invention, the low-frequency oscillation of the new energy synchronous machine grid-connected system can be effectively suppressed, and meanwhile, the situation that the grid-connected safety is threatened due to the great fluctuation of the terminal voltage of the motor caused by suppression measures is avoided.

The invention discloses a control method, device, equipment, medium and product of a network-forming type permanent magnet wind power system, and the method comprises the steps: calculating the maximum wind energy tracking power outputted by the network-forming type permanent magnet wind power system under the optimal wind energy tracking based on the maximum wind energy tracking coefficient; calculating a direct-current voltage damping control coefficient of a side damping controller according to the inertia coefficient and the damping coefficient of the direct-current voltage; calculating an electromagnetic power reference value output by the permanent magnet synchronous generator according to the maximum wind energy tracking power and the DC voltage damping control coefficient; and subtracting the electromagnetic power reference value from the electromagnetic power actual value, and inputting the difference value into a machine side active power controller so as to adjust the electromagnetic power output by the permanent magnet synchronous generator. According to the method, on the basis of not adding hardware equipment, the transient stability of the grid-forming type permanent magnet wind power system during the short-circuit fault period of the power grid can be remarkably improved only by changing the control strategy of the machine-side converter of the grid-forming type permanent magnet wind power system.

The invention discloses an active power control method for a flyback topology micro inverter system, and the method comprises the steps: calculating the load power of a load end through a current sampling module, and carrying out the uniform power distribution of a PV primary side branch when the load power is greater than or equal to the rated power of an inverter system; when the load power is smaller than the rated power of the inverter system, the PV primary side branch is closed step by step according to the load power difference; and when the load power is smaller than the minimum set power sum, one PV primary side branch is kept to operate. When the load power is smaller than the minimum set power, all the PV primary side branches are closed, and when the load power is larger than the minimum set power of the PV primary side branch with the lowest minimum set power, the system is started. According to the invention, multi-path regulation and control can be realized, and the control stability of the system is improved. And uniform distribution control, step-by-step adjustment distribution control, minimum power control and active power control are relatively flexible and efficient, so that the service life of the system is remarkably prolonged, and the reliability of the system is remarkably improved.

The invention relates to an alternating-current fault ride-through control method and device for a grid-forming type wind generating set. The wind generating set is arranged in a direct-current power transmission system based on a diode rectification unit, and the method comprises the steps that a voltage error value is determined based on a measured value and a reference value of output voltage of a converter of the wind generating set, and the reference value of the output voltage is an alternating-current side rated voltage amplitude of the diode rectification unit; adjusting an active power reference value and a reference frequency and a frequency measurement value of the output voltage based on the voltage error value; and performing active power control on the wind generating set based on the adjusted active power reference value, and performing frequency control on the wind generating set based on the adjusted reference frequency and the frequency measurement value. By adopting the method and the device, whether the fan enters the fault ride-through strategy or not can be determined by adopting the local information voltage amplitude without additional fault information, and the fault current of the converter can be reduced.

The invention relates to the field of power system protection and control, in particular to a vehicle-network interactive charging station self-adaptive fault ride-through method and device considering power grid voltage support, and the method comprises the steps: collecting the voltage amplitude of a grid-connected point of a charging station at a main protection action moment, and if the voltage amplitude of the grid-connected point recovers to be more than 0.95 times of rated voltage, judging whether the grid-connected point recovers to be more than 0.95 times of rated voltage; active power control of the voltage source converter is switched into direct-current voltage control at the main protection action moment, the reactive power reference value is adjusted to be consistent with that before the fault, and the charging station recovers normal operation, otherwise, the discharging power reference value of the charging station is adjusted to be Pmax 2 at the main protection action moment, and the charging station recovers normal operation. And meanwhile, active power control of the voltage source converter is switched into direct-current voltage control, and a reactive power control reference value of the voltage source converter is adjusted to Qmax 2 until the voltage of the grid-connected point of the charging station is recovered to be more than 0.95 times of rated voltage. Corresponding control strategies are adopted according to different fault severity degrees, and the method can adapt to different fault severity degrees, different initial operation working conditions and the access number of the electric vehicles.

The invention provides a network construction converter control method, which comprises the following steps: decoupling an original transient damping coefficient and an original primary frequency modulation coefficient which are mutually coupled in an original VSG control system to obtain an active steady-state primary frequency modulation coefficient K [omega] and an active transient damping coefficient KD, and further respectively establishing active steady-state and transient independent regulation channels; active control steady-state deviation is realized through an active steady-state primary frequency modulation coefficient K [omega], response speed control is realized by combining a controller function Gdamp (s), active transient damping coefficient KD is adjusted to be combined with a second-order filter function GLPF (s) to control active low-frequency oscillation suppression, and independent control and adjustment of active steady state and transient state are realized. The adaptability of a network-forming converter control strategy to different power grid intensities, system inertias and load characteristics is further improved, and the problems that in an existing VSG control method, the control effect coupling of an original transient damping coefficient and an original primary frequency modulation coefficient is too high, and the requirement for independent adjustment of active power dynamic and steady-state characteristics cannot be met are solved.

The invention discloses an active power control method, system, equipment and storage medium for an energy storage system of a power grid side energy storage power station, and relates to the field of energy storage power stations. Data are collected and processed through multiple channels, and power instructions of PCS are obtained through dynamic priority calculation, comprehensive power instruction synthesis and SOC optimization distribution; and then issuing through a GOOSE protocol and performing closed-loop correction according to feedback deviation of + / -2% dead zones, thereby realizing accurate regulation and control of active power. The system comprises a power grid dispatching module, an energy storage EMS module, a coordination control module and each energy storage system module, the response speed can be increased, the problem of battery imbalance is solved, the coordination stability with the power grid is enhanced, and the practicability is high.

The invention discloses a method, a device, equipment and a medium for enhancing transient stability of networking type energy storage, and relates to the field of power electronic stability, and the method comprises the steps: carrying out the improvement of an active power control structure of initial networking type energy storage based on power deviation feedback and angular frequency deviation feedback, so as to obtain an improved control structure; determining a feedback compensation coefficient in the improved control structure according to the rated angular frequency of the power grid and the steady-state power angle of the network-building type energy storage before fault ride-through; and determining the transient power angle deviation of the network construction type energy storage during the fault ride-through period based on a nonlinear perturbation theory, and controlling the transient power angle deviation to be zero by using the feedback compensation coefficient and a preset constraint condition so as to enhance the transient stability of the network construction type energy storage. Therefore, the power angle fluctuation and the frequency fluctuation of the network construction type energy storage during the fault ride-through period can be greatly reduced, and the transient stability and the frequency stability of the network construction type energy storage are improved.

The invention discloses an active power regulation and control method, device and equipment based on an electrochemical energy storage power station, and a medium, and relates to the technical field of active power control of the electrochemical energy storage power station, the regulation and control method comprises the steps: obtaining the required power and the current actual output of the whole energy storage power station, and according to the required power and the current actual output, obtaining the required power of the whole energy storage power station; determining an applicable power adjustment strategy to extract active output data of the whole station of the corresponding energy storage power station, and calculating a pre-running instruction corresponding to each energy storage converter in the whole station of the energy storage power station based on the active output data, the required power and the current actual output; and then the SOC margin of a battery stack controlled by the energy storage converter is used to correct each pre-operation instruction to obtain a corrected total station execution instruction so as to control the operation of each energy storage converter of the total station. According to the regulation and control method, instruction execution deviation caused by charging and discharging efficiency and real-time state difference can be effectively reduced, and accurate regulation and control of the active power of the energy storage power station and balanced operation of equipment are realized.

The invention provides a cooperative low-voltage ride-through control method and related device based on a network construction type and network following type three-terminal interconnection system, and the method comprises the steps: triggering a cooperative low-voltage ride-through control mechanism in response to a voltage drop fault generated at an AC side connected with a network construction type converter; performing cooperative control on each converter based on the mechanism; wherein the control network construction type converter only undertakes AC side voltage establishment and current safety survival functions, realizes current limiting control through adaptive virtual impedance, and does not participate in DC side energy adjustment of a common DC bus; the DC voltage control type grid-following converter is controlled to suppress DC voltage double-frequency fluctuation of the common DC bus, and actively absorb and compensate double-frequency power disturbance introduced by the grid-forming converter; and controlling the active power control type grid-following converter to avoid active power adjustment during the voltage drop fault period. A collaborative low-voltage ride through control mechanism is provided, the direct-current voltage fluctuation is reduced, and the overall low-voltage ride through capacity of the system is improved.

This invention discloses a series-parallel hybrid power flow control method and system, applied in the field of power grid power flow control. The method includes: determining power grid demand information based on key operating data of the transmission network; determining the equivalent active power control quantity of UPFC, the equivalent power flow regulation quantity of SSSC, and the equivalent reactive power control quantity of STATCOM based on the quantification results of the demand information, the first constraint data of the series-parallel hybrid power flow control device, and the second constraint data of the transmission network; and injecting equivalent voltage and equivalent current into the transmission network through the series-parallel connection of UPFC, SSSC, and STATCOM to regulate the key operating data of the transmission network. When power flow control is required in the transmission network, this invention injects controllable voltage and current into the transmission network through UPFC, SSSC, and STATCOM to achieve adaptive control of power flow on transmission network lines.

The invention discloses a coordinated optimization scheduling method for improving dynamic characteristics of a source storage response AGC regulation instruction. A frequency modulation performance index calculation method for a power generation unit to respond to an AGC instruction is deduced by researching transaction rules and policy documents of a domestic frequency modulation auxiliary service market, and a time-phased source-storage combined frequency modulation control strategy is designed according to the frequency modulation index calculation method. And then, an MOEA / D algorithm is utilized to optimize a micro-grid source storage optimal active power control strategy considering the power generation cost and the energy storage life under time-phased control. And finally, realizing coordinated optimization scheduling of each power generation unit under the optimal active power control strategy of the micro-grid based on model prediction control. The method can provide a reference for the source storage active power coordinated optimization scheduling of the micro-grid participating in the frequency modulation auxiliary service market.

A flexible loop-closing device and its active power control method are disclosed. The device includes a power electronic transformer and distribution networks connected to both sides. Each phase of the power electronic transformer includes several power modules symmetrically arranged on both sides. Each power module includes an H-bridge section composed of power electronic switching devices T1-T4 and a DAB section composed of power electronic switching devices T5-T8. The power modules on both sides are connected through a resonant inductor Lr and an isolation transformer T. The H-bridge sections of the power modules on the same side are connected in series to the high-voltage AC bus of the distribution network on the same side. The active power control method is as follows: the AC side of the loop-closing device is controlled by a cascaded H-bridge, and the DC side is controlled by a DAB. When there is no active power flow control requirement, the DAB section does not need to work, and the DC bus voltage of the power modules on both sides is controlled by their respective cascaded H-bridges. This method can simplify the operation complexity of the loop-closing device to the greatest extent, ensure the stable operation of the loop itself and the reliability of the system power supply, and greatly reduce the system losses when there is no active power flow control requirement. The active power control strategy proposed in this invention can avoid frequent switching of the cascaded H-bridge control mode, ensure the stable operation of the flexible loop-closing system, and improve the dynamic response speed.

The application provides a power flow inversion method of a direct current power transmission system, the direct current power transmission system comprising a power sending end and a power receiving end, the power sending end comprising a first converter, the power receiving end comprising an electrically connected second converter and at least one third converter, the type of the first converter being the same as that of the second converter, the type of the second converter being different from that of the third converter, the power flow inversion method comprising: determining whether the direct current power transmission system receives a power flow inversion instruction; in the case that the direct current power transmission system receives the power flow inversion instruction, obtaining a direct current voltage instruction value, and controlling the direct current voltage of the first converter to follow the change of the direct current voltage instruction value, the direct current voltage instruction value being stepwise reduced from a first predetermined value to a second predetermined value; controlling the active power of the second converter according to the direct current voltage of the first converter; and controlling the direct current of the third converter to remain unchanged. The method can overcome the complexity and current impact problem of the power flow inversion operation.