441 results about "Stability margin" patented technology

A new current loop control system method is proposed for a single-phase grid-tie power conditioning system that can be used under a standalone or a grid-tie mode. This type of inverter utilizes an inductor-capacitor-inductor (LCL) filter as the interface in between inverter and the utility grid. The first set of inductor-capacitor (LC) can be used in the standalone mode, and the complete LCL can be used for the grid-tie mode. A new admittance compensation technique is proposed for the controller design to avoid low stability margin while maintaining sufficient gain at the fundamental frequency. The proposed current loop controller system and admittance compensation technique have been simulated and tested. Simulation results indicate that without the admittance path compensation, the current loop controller output duty cycle is largely offset by an undesired admittance path. At the initial simulation cycle, the power flow may be erratically fed back to the inverter causing catastrophic failure. With admittance path compensation, the output power shows a steady-state offset that matches the design value. Experimental results show that the inverter is capable of both a standalone and a grid-tie connection mode using the LCL filter configuration.

The present invention relates to a power system and provides a method for considering the network security constraints of in the operation of economic dispatch of power systems, which comprises the power flow constraint of branches, the static voltage stability constraint and the transient stability constraint, and provides an effective way for coordinating contradiction between the economy and security of power system operation. The security region based security-constrained economic dispatching method comprises the following steps: step 1, calculating the coefficients for the active power static security region, the cut-set voltage stability region and the dynamic security region respectively; step 2: building the models for security region based security-constrained economic dispatch; step 3: solving the unit on/off state optimal sub-problem through Social Evolutionary Programming; step 4: calculating the generation cost, the static voltage stability margin and the transient stability margin in the dispatching period; step 5: obtaining a feasible economic dispatching scheme, otherwise, return to step 3. The invention is mainly applied in load dispatching optimization.

The invention discloses an active power control method of master station-end wind power field subject to wind power grid integration for a large-scale wind power integrated network, and belongs to the technical field of power systems. The method comprises the following steps of: providing a regional power grid active scheduling framework containing wind power field control, predicting newly increased functional short and ultra-short wind power by adopting the control principle of wind power-based predicted ''generating plan tracking'' serving as a main aspect and wind power unit ''direct frequency modulation participation'' serving as a secondary aspect, and describing auxiliary frequency modulation; providing data flow design of an active scheduling system containing wind power field control; providing a wind power field active power control mode to improve the wind power receiving capacity of the power grid by wind power participating power grid active control based on the current wind power control technology; and providing stable section-based wind power field active power control so as to further solve the wind power consume problem under high wind power permeability rate by using the renewable energy source such as maximum dissipated wind power and the like as principle on the premise of ensuring that the wind power of the system is connected to the important section stability margin.

Neural Network Loadflow (NNL) computation method is invented involving input vector composed of net nodal injection of real and reactive powers and diagonal elements of conductance and susceptance matrices multiplied by the squared voltage magnitude components of the flat-start normally used as initial solution estimate guess for loadflow solution by conventional NRL or SSDL methods. Training, and testing/validating input-output data sets are generated by applying uniform and non-uniform scaling factors applied to base case loads at PQ-nodes, resistance and reactance of transmission line branches. These scale factors are increased until loadflow solution by conventional methods such as Newton-Raphson Loadflow and Super Super Decoupled Loadflow methods diverge. Divergence of loadflow methods are due to node voltage, node angle, and numerical instabilities. Voltage magnitude and phase angle values in the solution before divergence are respective stability limits and voltage magnitude and phase angle values in loadflow solution provide direct measure to the respective stability margins. Also Suresh's diakoptiks based feature selection technique is presented for ANNs calculating one node variable with one neuron each in their output layers.

(A1) A turbofan engine control system is provided for managing a fan operating line. The engine (10) includes a spool having a turbine housed in a core nacelle (12). A turbofan (20) is coupled to the spool (14). A fan nacelle (34) surrounds the turbofan and core nacelle and provides a bypass flow path having a nozzle exit area (40). A controller (50) is programmed to effectively change the nozzle exit area in response to an undesired turbofan stability margin which may result in a stall or flutter condition. In one example, the physical nozzle exit area is increased at the undesired stability condition in which the airflow into the engine creates a destabilizing pressure gradient at the inlet side of the turbofan. A turbofan pressure ratio, turbofan pressure gradient, low spool speed and throttle position are monitored to determine the undesired turbofan stability margin.

The invention discloses a robust dicyclic photovoltaic grid-connected control method based on power feedforward, which mainly comprises three parts: proportion integration (PI) control of exocyclic voltage, dead-beat control of endocyclic robust predictive current and power feedforward control, wherein the exocyclic PI control of the voltage is used for stabilizing the capacitive voltage of a direct-current side; the dead-beat control of the endocyclic robust predictive current is used for carrying out linear prediction on the voltage of a power grid at a next control period and carrying out non-linear prediction on grid-connected current by advanced control so as to obtain the command value of the grid-connected current at the next period; and then, PWM (pulse-width modulation) and grid-connected control are realized by the dead-beat control. According to the robust dicyclic photovoltaic grid-connected control method based on the power feedforward, a photovoltaic grid-connected inverter has higher robustness, wider stability margin and quicker dynamic response, and the requirement of grid-connected running of an inverter is better met.

The invention relates to a self-adaptive screening method for an anticipated fault set in power system security and stability on-line assessment, which is suitable for determining the anticipated fault set in the static, transient and dynamic security and stability on-line assessment of the power system. The method adopts the core concept that the fault set required to be recalculated in the security and stability on-line assessment is determined according to the mode of the security and stability margin of all anticipated faults given by the security and stability on-line assessment in the previous round of the power network. The invention takes the power network security and stability margin and the security and stability mode as the quantitative index of the power network security and stability degree, takes the security and stability margin as the index, and screens the anticipated fault subset required to be recalculated from the anticipated fault universal set by combining the security and stability mode and the degree of change of the running state of the power network as the dynamic anticipated fault set which meets the practical demands of the engineering and is changed along with the running state of the power network; the scale of the anticipated fault set used for the security and stability on-line assessment under the current time section can be reduced, and the computing speed for the security and stability on-line assessment is increased.

The inventive method assesses the stability of an electric power transmission network, where said network comprises a plurality of substations, buses and lines, and a system protection center (8). It comprises the steps of 1. measuring phasor data (9) for voltages and currents at a plurality of locations of the network, 2. transmitting said phasor data (9) to said system protection center (8), 3. transmitting information (5) regarding the state of switches of at least one substation to the system protection center (8), and 4. the system protection center (8) determining at least one stability margin value of the transmission network. In this way, detailed real-time information about the state of the network is collected at a system level of the network, allowing a corresponding global analysis of the information. In a preferred embodiment of the invention, the system protection center determines one or more control commands (6), based on the phasor data (9) and on the state of switches. The control commands (5) are transmitted to at least one substation and executed there.

A method for measuring a stability margin at a node of a polyphase power grid injects suppressed-carrier stimulus into a node of the power grid by low-level amplitude modulation of the output voltage of a pre-exiting generator connected to the node. Response signals are obtained and product demodulated on a per-phase basis and summed in three-phase groups. Demodulated and summed responses contain signals that represent the suppressed-carrier impedance upstream and downstream of the stimulus injection point, and are processed to determine the stability margin at the node.

A power distribution system is dynamically and adaptively configured in real-time to improve energy efficiency, reliability and power quality, particularly if the system includes renewable sources and storages. An optimal multi-objective scheduling and partitioning method is provided to partition the system into self-sufficient sections (SSS) through optimally combination of adjacent basic switching sections (BSS). The SSSs enable system operating at a lower cost, with less power losses, more energy efficiency, improved power quality, and sufficient transient security. The method uses two storage based transient security indices, storage compensation power margin (SCPM) and storage compensation energy margin (SCEM) evaluate the transient stability margin of distribution system. A minimal stability margin is used to ensure that the system remains stable when subject to large unexpected load deviations.

The disclosure relates to a method of detecting and managing voltage instability in power systems operations. The disclosed method identifies and follows Thevenin and load impedance values as they fluctuate in a power system using synchrophasor measurements. The values are recursively estimated and entered into calculations to identify stability margins through a simple P-Q plane representation to determine if load shedding is necessary.

The invention relates to a section active control strategy analysis method for online stability margin evaluation. The method comprises following steps: determining power distribution section compositions, online state evaluation data and an adjusting and managing range, carrying out network topology analysis, automatically generating section sending end region, section receiving end region and control generator set; calculating the sensitivity of each section branch through using direct current load flow according to online stability margin evaluation rational and safe rules, generating a section active comprehensive sensitivity; screening the section control generator set according to the value of the comprehensive sensitivity, through comprehensively considering the actual output, the operation state and the adjustable output upper limit constraint conditions of a generator, searching to generate a sending end adjustable generator set and a receiving end adjustable generator set; calculating the power adjusting amount of an adjustable generator and generating the section active control strategy for online stability margin evaluation. According to the method of the invention, the problem that the existing online stability margin evaluation functions depend more on dispatching the off-line calculating experiences of specialists and cannot carry out self-adaption to the changes of the operation modes of a power grid is solved.

The method includes following steps: obtaining online data of power network from energy management system and power market; determining probability of equipment fault in the time period based on arrangement of equipment repair and weather condition in each area; creating sample space from Monte Carlo simulation, each sample includes two parts: X (increment direction of power), and Y (set of fault equipment); calculating steady tolerance of voltage corresponding to each sample and obtaining probability density distribution of voltage of voltage in power system from layered computation method; determining value of steady tolerance system needed to reach, limiting values of system parameters, and precaution control value; adjusting working parameters of system to ensure steady voltage in power system under specified confidence level. Advantages are: getting rid of a great lot calculation in traditional 'point-by-point method' and avoiding CPF calculation again.

The invention provides a static voltage stability margin analyzing and system fault ordering method of a power system. The static voltage stability margin analyzing and system fault ordering method includes the following steps that the Newton iteration method based on the optimal multiplier is used for determining a static voltage collapse point; according to the characteristic of iteration convergence, the type of the voltage collapse point is judged; according to the requirement for stability margin, system fault danger conditions are checked and ordering of stability faults is performed; the faults are parameterized and the iteration method is used for giving out the order of seriousness degrees of instability faults. According to the static voltage stability margin analyzing and system fault ordering method of the power system, voltage stability margins of the power system can be rapidly given online, real-time effective monitoring is carried out on the voltage stability and the comprehensive order of the stability faults and the instability faults can be used for guiding a power generator to adjust online and switching reactive power compensation devices when the system encounters faults, can also guide sub-circuit parameter adjusting, line increasing and decreasing, configuration of an FACTS device and the like off line and have great significance in operation and planning of the power system.

The invention relates to a method for adaptively controlling hybrid damping of a grid-connected inverter applicable to weak grid access conditions. Most existing methods are used for optimally controlling fixed impedance of grids at present, but grid access conditions of grid-connected inverters are dynamic and varied, so that adaptive control under different grid impedance conditions has high application value. The method includes measuring impedance information of a weak grid by a harmonic injection process; enabling a controller to adaptively modify loop parameters and active damping coefficients; ensuring a wide stability margin and a proper control bandwidth of a control system. The method has the advantages that the novel method for adaptively controlling the hybrid damping is based on real-time measurement on impedance of the grid, and optimal control parameters in a DSP (digital signal processor) are automatically selected, so that the control bandwidth and a phase margin of the inverter under different grid impedance access conditions can be guaranteed, and the grid-connected inverter can safely and reliably run under the various grid impedance conditions.

The invention discloses a method for controlling a grid-connected inverter based on feed-forward compensation. The method comprises the following steps of: (1) acquiring a grid voltage, a grid side current and a capacitance current; (2) according to the grid side current, generating an instruction signal; (3) according to the grid voltage and the capacitance current, acquiring a current feed-forward signal and a voltage feed-forward signal; and (4) superposing the instruction signal, the current feed-forward signal and the voltage feed-forward signal to obtain a modulation signal, and generating a switching signal for controlling the grid-connected inverter according to the modulation signal. The method has the advantages that: a second-order differential feed-forward item of the grid voltage is compensated by a first-order differential feed-forward link of the capacitance current, so that a third-order system is reduced to a first-order system, the stability margin of the system is improved, the design process of a current regulator is simplified, and the grid side current cannot be influenced by grid voltage harmonic waves.

The invention discloses a method for recognizing a transmission section power limit interval of power system transient stability, which comprises the steps of: respectively carrying out transient security stability evaluation on faults in a transmission section transient security stability check fault set by adopting a transient angle stability quantitative evaluation method and a transient voltage security stability quantitative evaluation method to obtain a transient angle stability mode and a transient voltage security stability mode of each fault; respectively calculating impact factors of each generator and each load to the transmission section power limit according to participation factors of the generators and the load, the sensitivity of the power to the transmission section power, the transient angle stability margin and the transient voltage security stability margin; and calculating the minimum value and the maximum value of the transmission section power limit through regulating powers of the generators and the loads according to the impact factors of the generators and the loads to the transmission section power limit.

The invention discloses a new energy available capability assessment method considering transient security constraints, belongs to the field of new energy available capability assessment. According to the invention, on the basis of the EEAC theory, transient security constraints are added into an existing new energy available capability assessment method; and on the basis of the existing assessment method with peak and frequency modulation constraints as reference, full consideration is given to the transient security stability constraints of an outgoing channel, the transient power angle stability margin, transient voltage security margin and transient frequency drop acceptability margin are quantified, and the unit adjustment sequence is determined according to the magnitude of sensitivity of the output adjustment of a new energy unit under a buckling mode. The invention is capable of achieving optimal output adjustment of the new energy unit under a transient buckling forbidden faulty set, and meanwhile achieving the new energy grid-connected maximum availability while satisfying safe and stable operation of a power grid.

The present invention is a novel device, system, and method for simultaneous selection of filters and loop proportional gain for a closed loop system. According to an exemplary embodiment of the present invention, a method provides an automated selection of the portion of the controller known as the speed loop compensator. The method may operate on a frequency response function that represents the dynamic response from an actuation force (e.g. motor torque) to the sensor used for feedback of speed control (e.g. motor encoder angle). The frequency response function may be represented as a series of complex numbers each with a corresponding frequency value. The tuning method determines the combination of filter parameters that allows the loop proportional loop gain (K_p) to be maximized while meeting a specified set of criteria for stability margins. Methods for selecting integral gain and reference model are also presented.

The invention belongs to the technical field of the calculation and analysis of a power system, and discloses a method for comprehensively evaluating the precision of stability calculation models and parameters based on PMU data. The method comprises the following steps: performing time-domain simulation on an electromechanical transient process and an electromechanical dynamic process for the disturbance of a power grid, and adopting a power system security and stability quantitative analyzing method to calculate transient security and stability margins, modes, dynamic oscillation damping ratio and frequency; (2) adopting PMU actually-measured data on the power angle and frequency of a generator and the voltage and frequency of a busbar after the disturbance of the power grid to take place of time-domain simulation results of corresponding physical quantities, and then adopting the power system security and stability quantitative analyzing method to calculate the transient security and stability margins, the modes, the dynamic oscillation damping ratio and the frequency; and (3) comprehensively evaluating the precision of transient and dynamic security and stability calculation models and the parameters by comparing differences between the two transient and dynamic security and stability margins and the modes. Through the method, reliability evaluation on the transient and dynamic security and stability simulation calculation results of the power system is realized.

The invention provides an online practical quantization evaluation method of transient state stability of a power grid based on a WAMS (wide area measurement system) and a unit pair and belongs to the technical fields of online monitoring and early warning safety and stability of the power grid based on the WAMS. The method comprises the steps of: screening a generator set omega of which the power grid is distributed most severely relatively based on the wide-area measurement information of the WAMS, wherein setting any two generators within omega equivalent to a stand-alone system; and constructing a dynamic relative transient stability margin index (DTSI) on the basis, wherein the DTSI of the smallest unit pair is taken as the DTSI of the power grid. According to the invention, response track information is actually measured based on the power grid, and a dynamic relative idea is adopted. The method is suitable for any complicated model or transition mode of the power grid; the information can be effectively measured by fully utilizing a PMU (power management unit); the problems of coherent generator identification, curve fitting and energy integral hypothesis path and the like are avoided, and the method is less in calculated amount and high in reliability, and is expected to be applied to online safety monitoring and early warning engineering of the power grid based on the WAMS.

The invention relates to a transient voltage stable on-line assessment method based on a WAMS (Wide Area Measurement System) and an EMS, comprising: obtaining WAMS real-time power grid measurement information to determine whether a power grid is disturbed; obtaining the topological structure, parameters and power flow operation information of a current power grid from an EMS when the power grid is disturbed so as to calculate a full admittance matrix concerning load equivalent admittance; according to the WAMS measurement information, running statistics on nodes having a voltage dip exceeding a preset threshold value, obtaining Thevenin equivalent parameters of statistic nodes based on full admittance matrix inversion to be used as an initial value to track Thevenin equivalent parameter identification of the WAMS measurement information and static state voltage stable margin index calculation, and calculating a transient voltage dip acceptability area index; and running statistics on nodes having a power grid node voltage dip exceeding a preset threshold value and having a dip duration greater than a preset threshold value, and determining the occupancy of power grid disturbance transient voltage instability nodes. The method can rapidly and effectively realize the stable and rapid assessment of a transient voltage.