366 results about "Reactive power control" patented technology

The invention relates to the technical field of power electronics, in particular to a photovoltaic off-grid inverter control method and system, and the method comprises the following steps: applying a test signal to identify an output interaction characteristic parameter, predicting the power generation power through combining with weather and attenuation, calculating the power fluctuation, and adjusting a current control parameter set. And calculating voltage and reactive power compensation parameters to generate an inverter control instruction, and combining a temperature load prediction trend to adjust a power allowable value to obtain a predictive power calibration coefficient. According to the invention, by analyzing the output interaction characteristics, enhancing the perception capability of the inverter to the actual operation environment, combining with the prediction of the photovoltaic power generation amount, realizing the prediction and influence evaluation of the power fluctuation, improving the adaptive adjustment capability of the current control parameters, improving the output voltage and reactive power control precision by utilizing the interaction characteristics, and optimizing the electric energy quality; and through thermal management of multi-point temperature and load prediction, the operation safety is improved, the service life of equipment is prolonged, and the operation performance of the photovoltaic off-grid system in a complex environment is improved.

The present application provides a reactive power feedback control-based control method for a commutation failure in a hybrid cascaded high-voltage direct-current power transmission system, a storage medium and an electronic apparatus, and particularly relates to a reactive power feedback control-based control method for a commutation failure in a hybrid cascade high-voltage direct-current power transmission system. The method mainly comprises the following steps: acquiring power data of a hybrid cascaded high-voltage direct-current power transmission system; calculating the reactive power supply of an inverter-side MMC-end alternating-current system, the reactive power supply of an inverter-side alternating-current filter, and the reactive power supply of an inverter-side LCC-end alternating-current system; solving a reactive power control instruction of an inverter-side MMC converter; and, on the basis of a critical voltage, determining whether to implement the reactive power feedback control-based control method for a commutation failure in the hybrid cascaded power transmission system. The method can effectively reduce the probability of commutation failures in hybrid cascaded power transmission systems, thus guaranteeing safe and stable operation of large-scale power grids.

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 invention discloses an optimized reactive power control and fault ride-through method and system for a hybrid commutation converter, and the method comprises the steps: introducing reactive power control and considering the constant voltage control of negative turn-off angle limitation, achieving the control of an extremely low turn-off angle through the active turn-off of a full-control device in the converter under a steady-state working condition, and further meeting the demands of a high power factor; the investment of passive filter equipment is reduced; under the alternating current fault working condition, forced commutation and negative turn-off angle operation are achieved through active turn-off of a full-control device, the receiving end power grid voltage is effectively supported while commutation failure of a half-control thyristor in the hybrid commutation converter is avoided, and the active power transmission level during the fault period is improved. The full-control characteristic of the reverse blocking type integrated gate commutation thyristor in the hybrid commutation converter is fully utilized, reactive power control under the steady-state working condition and stable power transmission under the alternating-current fault are achieved by optimizing active turn-off control, and the method has wide applicability and good application prospects.

The invention relates to the technical field of new energy power system control, and relates to a power decoupling method for cooperative control of voltage feed-forward compensation and adaptive virtual impedance. The method comprises the following steps: acquiring a power grid current and a power grid voltage, and calculating a reactive power measured value and an active power measured value of a power grid; virtual synchronous machine control is carried out, and a voltage feed-forward pre-compensation item is introduced into a reactive power control loop; calculating a reactive power control loop after VSG compensation, and obtaining VSG output side voltage and instantaneous angular frequency; self-adaptive virtual impedance control is adopted, a self-adaptive virtual impedance reference value is calculated, line impedance is dynamically adjusted, and a voltage loop input instruction voltage is calculated according to the line impedance; and adjusting the output performance of the inverter according to the instruction voltage. According to the invention, the problem of power fluctuation caused by VSG output voltage amplitude variation is effectively solved, and the dynamic influence of a power coupling item is weakened.

The invention discloses a virtual power plant voltage-reactive power coordination control method based on fusion of a graph neural network and deep reinforcement learning, and the method comprises the steps: explicitly introducing a topological structure of a power distribution network into the state representation of deep reinforcement learning in the form of graph data, and extracting and processing the graph structure data through the graph neural network; topological correlation and dynamic interaction among nodes in a power grid are accurately captured; and the extracted graph features and the traditional system state quantity are fused and input to the deep Q network for learning and decision making, so that the optimal coordination control of the distributed resources in the virtual power plant and the power distribution network equipment is output. The virtual power plant voltage-reactive power control method and device aim at solving the problem that in the prior art, perception on a power grid structure is insufficient, and the decision-making precision and robustness of virtual power plant voltage-reactive power control and the adaptability in a large-scale complex power distribution network are remarkably improved.

The invention provides a grid-connected power detection method and detection system for a three-phase four-wire photovoltaic grid-connected energy storage system. The method comprises the following steps: obtaining a total reactive power instruction according to a grid-connected total active power instruction and a reactive power control mode; calculating to obtain single-phase active power and single-phase reactive power of the power grid; performing closed-loop control according to the total reactive power instruction, the single-phase active power and the single-phase reactive power to obtain a control signal of closed-loop output; and performing grid-connected control on the inverter according to the control signal to obtain grid-connected active and reactive output. According to the method, starting from power definition, phase current is projected to a phase voltage direction and an orthogonal direction, deformation of product sum and difference is utilized, and active current and reactive current are averagely extracted through a periodic sliding window to obtain active power and reactive power, so that three-phase active and reactive independent decoupling control is realized; and the method can adapt to working conditions of unbalanced power grids and unbalanced power requirements.

Provided in the present disclosure are a converter system of a wind turbine generator system, and a wind turbine generator system and an offshore wind farm. The converter system comprises: a voltage source converter and a current source converter; and a converter control apparatus, which is configured to control the operation of the voltage source converter and the current source converter by means of taking into account an internal circulating current of a wind turbine generator system in voltage outer-loop control of the voltage source converter and by means of taking into account the internal circulating current in active and reactive power control stages of the current source converter.

The invention discloses an SLCC dynamic self-adaptive harmonic compensation control method, system and equipment and a medium. The method comprises the following steps: acquiring a three-phase alternating current on a common coupling point of a commutation converter and a static var filter device, a three-phase alternating current on a bridge arm branch of the static var filter device and a fundamental frequency control voltage of a fundamental frequency reactive power control loop; based on the number of converter valve pulses, extracting the three-phase alternating current on the common coupling point and the three-phase alternating current on the bridge arm branch to obtain a specified subharmonic suppression current instruction and a specified subharmonic suppression voltage; calculating based on the specified subharmonic suppression voltage and the fundamental frequency control voltage to obtain a bridge arm modulation voltage of the static var filter device; harmonic compensation is carried out on the multi-source self-adaptive commutation direct current sending-out system based on the bridge arm modulation voltage; the harmonic current generated by the common point can be eliminated through extraction and suppression of the harmonic current of the common point, the power quality of grid connection of the direct-current converter valve is remarkably improved, and the precision and stability of harmonic compensation are improved.

The embodiment of the invention relates to a dynamic reactive power control method and device for a new energy plant station, and the method comprises the steps: calculating a dynamic safety domain of virtual impedance based on a real-time estimation value of power grid impedance; based on a multi-time scale reinforcement learning algorithm, generating a virtual impedance control quantity under the constraint of the dynamic security domain; obtaining a reactive power output error value, and correcting the virtual impedance control quantity by using the reactive power output error value; and performing reactive power output control on the inverter of the plant station based on the corrected virtual impedance control quantity. According to the technical scheme provided by the embodiment of the invention, the power grid impedance is predicted through the multi-time scale reinforcement learning algorithm, the virtual impedance control quantity is generated accordingly, the upper layer prediction model can predict the impedance change trend in advance and provide a prospective reference for lower layer dynamic correction, and the lower layer dynamic correction model can realize instantaneous disturbance suppression. And rapid fine tuning of the virtual impedance is realized, so that more accurate virtual impedance control quantity can be obtained.

The invention relates to the technical field of power grid energy storage control, and particularly discloses a network construction type energy storage system and a control method thereof, and the system comprises a parameter collection module which obtains the voltage, frequency, short-circuit capacity ratio, phase angle and other power grid operation parameters of a grid-connected point in real time; the scene recognition module judges the power grid scene of the energy storage system according to the acquired parameters, wherein the power grid scene comprises a weak power grid scene, a fault scene, an oscillation scene, a phase angle jump scene and a power loss scene; the strategy library module stores control strategies for each scene, including active / reactive control, active / reactive decoupling, overload support, low-frequency oscillation suppression, phase angle stabilization and black start strategies; and the adaptive control module retrieves and calls a corresponding strategy from a strategy library according to an identification result, performs adaptive control on the energy storage system, and realizes intelligent response and stable support for a complex power grid environment. According to the invention, intelligent response and stable support of the energy storage system to a complex power grid environment are effectively realized.

Systems and methods for supplying power (both active and reactive) at a medium voltage from a DCSTATCOM to an IT load without using a transformer are disclosed. The DCSTATCOM includes an energy storage device, a two-stage DC-DC converter, and a multi-level inverter, each of which are electrically coupled to a common negative bus. The DC-DC converter may include two stages in a bidirectional configuration. One stage of the DC-DC converter uses a flying capacitor topology. The voltages across the capacitors of the flying capacitor topology are balanced and switching losses are minimized by fixed duty cycle operation. The DC-DC converter generates a high DC voltage from a low or high voltage energy storage device such as batteries and / or ultra-capacitors. The multi-level, neutral point, diode-clamped inverter converts the high DC voltage into a medium AC voltage using a space vector pulse width modulation (SVPWM) technique.

The invention discloses a power oscillation suppression method and a power oscillation suppression system for a multi-construction-network type converter parallel system, which relate to the technical field of converter control and comprise the following steps of: acquiring voltage, current and voltage frequency output by a three-phase converter at a grid-connected point in the multi-construction-network type converter parallel system; calculating active power and reactive power and inputting the active power and the reactive power into the virtual oscillator; according to the voltage frequency and the rated frequency, system power reference compensation is obtained through an introduced proportional differential controller, then the active power and an active power reference value are combined, frequency deviation is obtained through an active droop link of a virtual oscillator, and then a voltage phase angle is obtained through calculation; meanwhile, the reactive power is subjected to a reactive power control link of the virtual oscillator to obtain a voltage amplitude; and calculating a system reference voltage according to the voltage amplitude and the voltage phase angle, and performing real-time adjustment on the output of the three-phase converter through voltage and current double-closed-loop adjustment and PWM (Pulse Width Modulation) control so as to suppress the frequency oscillation of the system.

The invention discloses an energy storage type SOP black-start method, system and device based on improved VSG network construction control and a medium, and relates to the field of power grid black-start, and the method comprises the steps: an energy storage type converter MMC carries out the active and reactive control based on an improved VSG network construction control strategy; a non-fault side MMC is controlled to firstly close an isolation circuit breaker and slowly charge a direct-current capacitor, and when the voltage reaches a set threshold value, a current-limiting resistor is quitted; the fault side MMC is started by the same step as the non-fault side MMC; after synchronization is completed, AC circuit breakers between the non-fault side MMC and the feeder load and between the fault side MMC and the feeder load are closed respectively; based on the collected power grid power data, MMC output parameters are adjusted to meet the power grid connection condition, the control mode is switched according to the grid connection state, and the black start process is ended. And by arranging the black start resistor for current-limiting charging and sub-module voltage balance control, the phenomena of overcurrent and voltage unbalance in the black start process are avoided.

The invention discloses a variable frequency phase shift control DAB type single-stage inverter reactive power control method, system and device and a medium, and belongs to the technical field of power electronic converter control, and the method comprises the steps: setting a reactive power instruction as zero; when the reactive power instruction changes, the active power instruction and the reactive power instruction at the current moment are decomposed into a direct-axis current reference value and a quadrature-axis current reference value respectively; comparing the reference value with an actual sampling value, calculating an error compensation amount by using a PI controller, and determining the amplitude and phase of the AC side current according to the compensation amount; according to the amplitude and the phase of the voltage and the current, a DAB frequency conversion phase shift control curve is calculated; and generating a PWM (Pulse Width Modulation) signal according to the frequency conversion phase shift control curve obtained by calculation, wherein the PWM signal is used for driving a DAB inverter to carry out power transmission. According to the invention, on the premise that no extra hardware circuit is introduced, dynamic adjustment and accurate control of the instantaneous reactive power of the AC output side can be realized.

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.

A method for regulating voltage of electric power provided by an energy plant coupled to an electric power grid, the energy plant having at least one inverter-based resource ("IBR") coupled to the electric power grid via at least one inverter, the method comprising: using a control system communicatively coupled to an inverter of an IBR, implementing an automatic voltage regulator ("AVR") in the control system, the AVR having selectable control modes including a voltage control mode, a reactive power control mode, and a power factor control mode; receiving one or more command messages at the AVR for selecting a control mode; generating one or more command messages for controlling operations of the inverter; and, transmitting the one or more command messages for controlling operations of the inverter from the AVR to the inverter of the IBR for controlling operations of the inverter in accordance with the control mode selected.

The invention discloses a network construction type energy storage transient stability optimization control method and system considering reactive power degradation, and belongs to the field of power system transient stability control. According to the method, a network construction type energy storage grid-connected system model is constructed, a reactive power degradation effect dynamically triggered by a reactive power control loop is analyzed, and an active power loop optimization control equation is established according to the reactive power degradation effect. On the basis, a self-adaptive torque adjusting module is embedded in an active control module, and when it is monitored that the internal voltage of the inverter is reduced to 50% of a rated value, the reference torque is automatically and dynamically corrected so as to improve the power angle transient stability margin of the system. Simulation results show that the method can effectively restrain the instability of the network construction type energy storage power angle, obviously enhance the transient stability of the system, and guarantee the safe and reliable operation of the power grid.

The invention discloses a distributed power supply-based control method, system, equipment and medium, and relates to the technical field of distributed power supply control, and the method comprises the steps: collecting and preprocessing the real-time data of a distributed power supply, training a prediction model to optimize parameters, obtaining a load demand and power generation capability estimation, and adjusting the power based on a prediction result. Distributing active power according to a total load and a power contribution factor; setting a target power factor to calculate reactive power; monitoring voltage and load changes of a power grid in real time; dynamically selecting and adjusting a reactive power control strategy; and visualizing the running state and backing up the data to a database. Through closed-loop cooperation of data prediction, dynamic power control, value-oriented intelligent operation and maintenance and visual management, the stability, electric energy quality, operation and maintenance economy and management efficiency of the distributed power supply system are comprehensively improved.

The invention relates to the field of power grid voltage reactive power control, and discloses a three-level collaborative power grid voltage reactive power control architecture and control method.The architecture comprises an edge layer, a region layer and a master station layer, the edge layer is deployed at a key node of a power distribution network, and the region layer is deployed at a key node of the power distribution network; quick sensing and response to voltage fluctuation are realized by adopting thousand-time / second-level sampling and millisecond-level local calculation; the regional layer realizes cross-node reactive collaborative optimization based on a digital twinborn model and a federated learning framework; the master station layer constructs a voltage-reactive sensitivity matrix and dynamically adjusts the control weight of the edge layer. According to the control architecture and the control method, the advantages of centralized and distributed control are considered, the problems of response delay, collaborative conflict and data safety of traditional control are solved, the safety, the stability and the economical efficiency of the power grid in a high-proportion new energy access scene are effectively improved, and the control architecture and the control method are suitable for voltage reactive power control of the power grid in a complex region.

The invention provides a DRU-MMC sending end AC fault ride-through method and system, and the method comprises the steps: enabling a receiving end MMC to maintain the DC voltage to be constant in an outer loop fixed DC bus voltage / reactive power control mode during normal operation; sampling a sending-end AC power grid voltage effective value in real time, and calculating a deviation between the effective value and a nominal value; if the deviation shows that the voltage is lower than 90% of the nominal value (determining a fault), calculating a receiving end MMC direct current bus preset voltage instruction value according to the relation between the alternating current voltage and the direct current voltage; and the outer loop voltage control module is switched to a direct current bus preset voltage / reactive power control mode, and the direct current voltage is adjusted to a preset value by adjusting the input number of the sub-modules, so that closed-loop control is formed. According to the invention, continuous power transmission during a fault period can be realized, and the problem of off-network of new energy equipment caused by power congestion in a traditional scheme is avoided.

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 discloses a short-time voltage fluctuation suppression method, device and equipment based on partition fluctuation evaluation, and relates to the technical field of power system control. The method comprises the following steps: under a minute-level time scale, taking the comprehensive minimization of active power loss, voltage fluctuation in adjacent time periods and reactive power regulation cost as a target, constructing a multi-period reactive power voltage optimization control model, and obtaining a reference voltage and a reference reactive power control quantity; a power system is partitioned through a modularity-based reactive voltage control robust partitioning algorithm, and influence areas which are mainly influenced by new energy fluctuation are identified on the basis of partitioning. And constructing a partition fluctuation evaluation index and setting a partition optimization event triggering mechanism. And under a short-time scale, constructing a subarea reactive voltage optimization control model based on quadratic programming by utilizing a subarea space decoupling technology, and executing subarea coordination optimization. And correcting the partition reactive voltage optimization control model through a model correction method based on multiple linear regression.

The invention discloses a static var generator simulation method, a static var generator simulation device and a medium. The method comprises the following steps: constructing a constant voltage control model, a constant reactive power control model, a fault ride-through control model, an off-network protection model and a mode switching control model; constructing a static var generator simulation model based on the constant voltage control model, the constant reactive power control model, the fault ride-through control model, the off-network protection model and the mode switching control model; on the basis of the static var generator simulation model, reactive current is output to power grid equipment according to the specified voltage or reactive control target and the input control parameters, and the power grid equipment stably operates on the basis of the reactive current.

The invention provides a distributed power supply and energy storage reactive power control method considering interval coordination, and relates to the technical field of energy storage, and the method comprises the steps: dividing a power distribution network into a plurality of power distribution network regions according to the power loss, the power utilization demand mode, the load characteristics, and the power grid adjustment capability; collecting power loss data of branches in each power distribution network region; constructing a target power optimization model according to the power loss data and the power distribution coefficient corresponding to each power distribution network region; performing iterative solution on the target power optimization model by taking the total loss of the minimized current at each intersection as a target and taking branch node voltage constraint, reactive current stability constraint and equipment capacity constraint as constraint conditions to obtain a reactive power control strategy of the distributed power supply and energy storage; and according to the reactive power control strategy, controlling operation equipment in each power distribution network area. According to the scheme, control over the distributed power supply and the energy storage reactive power can be achieved through line monitoring, and then the voltage quality of the transformer area is improved.

The invention provides an offshore wind power direct current sending-out system structure based on an S7 bridge arm current source converter and a control method of the offshore wind power direct current sending-out system structure. The topological characteristic provided by the invention is that an S7 bridge arm is connected in parallel with the direct current side of the 6-pulse CSC, and the switch of the S7 bridge arm and the switch of each bridge arm of the 6-pulse CSC are distributed, so that multi-active and multi-reactive independent control is realized. The active quantity of the land CSC is controlled by constant direct current voltage, and the reactive quantity of the land CSC is controlled by reactive power. When the collected submarine cable has a fault, the S7CSC reduces the reference value of the AC bus and reduces the current fed by the CSC to a fault point, thereby preventing fault transient overcurrent and realizing fault ride-through. The technical scheme provided by the invention has the advantages that: S7CSC has two control degrees of freedom, can realize independent control of active components and reactive components, stabilizes the offshore AC voltage and frequency, can adapt to the fluctuation of wind power output, effectively inhibits the increase of fault current at the offshore AC collection fault, and realizes fault ride-through.

The provided is a reactive power optimization method for a power system based on distributed interval optimization, including following steps: S1. constructing a first model, where the first model includes an interval reactive power optimization model of a power system with a high renewable energy penetration rate, and the interval reactive power optimization model includes an objective function, a first constraint, and a constraint of an interval power flow equation; S2. obtaining a first state variable interval based on the constraint of interval power flow equation and a distributed interval power flow algorithm; S3. Converting the first model based on the first state variable interval and a security limit definition method, and obtaining a second model, where the second model includes a deterministic optimization model; and S4. obtaining a voltage and reactive power control strategy based on the second model and a primal-dual interior point method.

The invention discloses a fault cooperative reactive power control method and device for a wind and light station, and relates to the technical field of automatic control of a power system. According to the method, the optimal support for the grid-connected point voltage of each station can be realized when the fault occurs, and meanwhile, the wind and light station can output certain active power when the fault occurs, so that the system frequency is supported, and the fault control flexibility of the wind and light station is remarkably improved.

The embodiment of the invention discloses a photovoltaic inverter low-voltage ride-through control method and device, electronic equipment and a storage medium. The method comprises the following steps: acquiring a grid-connected point voltage and a direct-current side voltage of a photovoltaic inverter; judging whether the grid-connected point voltage is greater than a first threshold value or not; if the grid-connected point voltage is greater than the first threshold value, controlling the photovoltaic inverter to adopt constant direct current voltage control and constant reactive power control; if the grid-connected point voltage is not greater than the first threshold value, judging whether the photovoltaic inverter enters a low-voltage ride-through state or not according to the size of the direct-current side voltage so as to perform control switching; according to the low-voltage ride-through strategy of the photovoltaic inverter, a direct-current voltage criterion is added, so that the direct-current voltage can be recovered to a normal value under a low-voltage condition.

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.