238 results about "Voltage instability" patented technology

An electrochemical cell has two terminals. One of the terminals is connected to a pulse-width-modulated (PWM) power supply and to a voltmeter. The other terminal is connected to circuitry capable of switching between amperometric and potentiometric measurement modes. A sequence of successive approximations permits selection of a PWM duty cycle giving rise to a desired voltage at the terminal connected with the power supply. In this way a stable excitation voltage is supplied to the cell even in the face of supply voltage instability or drift or instability in electronics coupled with the cell.

The invention relates to an emergency protection circuit device capable of completing automatic switching when an AC-DC power grid is in an abnormal state, and in particular relates to an intelligent warning and control method dedicated for ensuring safety and stability of the power grid. The method comprises the steps that: an intelligent control master station acquires real-time data of the power grid through an EMS (energy management system), and an intelligent control substation in each zone real-timely monitors the bus voltage of the zone, power-receiving channel overload, main transformer overload in the zone and voltage instability of the power grid in the zone, and starts the power grid safety and stability control operation; the acquired real-time data of the power grid is integrated with the information uploaded by each substation to real-timely form tide section data of the power grid, and the safety and stability of the power grid are evaluated online; and safety and stability early-warning information of the power grid is provided by using the real-time operation data of the power grid to realize safe and stable control of the power grid and to realize the function of the second line of defense of the power system. The method provided by the invention can ensure safe and stable operation of the power grid by regulating a stability control device according to the running condition of the power grid.

Abstract of the DisclosureAn electrochemical cell has two terminals. One of the terminals is connected to a pulse-width-modulated (PWM) power supply and to a voltmeter. The other terminal is connected to circuitry capable of switching between amperometric and potentiometric measurement modes. A sequence of successive approximations permits selection of a PWM duty cycle giving rise to a desired voltage at the terminal connected with the power supply. In this way a stable excitation voltage is supplied to the cell even in the face of supply voltage instability or drift or instability in electronics coupled with the cell.

An LCD device is disclosed, to minimize the signal distortion by decreasing the instability of voltage in a—Si:H TFT of a gate driving signal output unit, which includes a signal controller for outputting first and second control signals Q and / Q; a pull-up transistor between a clock signal terminal CLK and a gate driving signal output terminal for receiving the first control signal Q, the pull-up transistor having a first gate electrode, a first source electrode and a first drain electrode, wherein the pull-up transistor has an asymmetric structure in a first area of the first source electrode overlapped with the first gate electrode and a second area of the first drain electrode overlapped with the first gate electrode; and a pull-down transistor connected between the gate driving signal output terminal and a ground voltage terminal, wherein the pull-down transistor receives the second control signal.

The present invention relates to a method of identifying the voltage stability of power grid in real time via figuring out the weak links of power grid; and uses a basic line voltage stability index BLSI or an extended line voltage stability index ELSI which is improved on the basis of the BLSI index to monitor, identify and judge power grid. The steps of identifying are as follows. Firstly, the requisite real-time date can be obtained via a PMU system or SCADA and EMS; Secondly, useless measurements get filtrated; thirdly, the parameters of the line are reassessed in real time if necessary in a given time interval; fourthly, a BLSI index or ELSI index is used to identify the weak links of the system; lastly, the system emergency protection control is started up to avoid the breakdown of system voltage at the BLSI value or ELSI value which is the weakest link that leads to voltage breakdown. The present invention has the advantages of identifying voltage invariability of the system in real time and weak lines and weak links that cause voltage breakdown of the system; and automatically dealing with actual loading properties relevant to voltage or frequency.

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 present invention provides an analysis method for an electrical power system whereby the plurality of buses are grouped into agents, family lines of agents and families of agents based on the reactive reserves depleted when the buses are loaded. Contingencies are then applied to the electrical power system and the reactive reserves are monitored and an exhaustion factor is determined for one or more family lines in one or more families. A method for selecting double outage that have no solution for each outage that has no solution when the outage is removed in small steps and an additional step has no solution. The boundary case solution is used to assess where, why, and how the contingency causes voltage instability, voltage collapse, and local blackout. Based on this information, the design of voltage rescheduling, active rescheduling, unit commitment, load shedding is determined that can be used as preventive, corrective, or emergency controls in applications such as system design and planning, operation planning, reactive and voltage management, real time control, and Special Protection System Control. Based on this information, solutions can then be applied to the political power system.

The invention provides a method for analyzing the stability of a power system by considering the change characteristic of a load. System instability can be differentiated to belong to angle instability, voltage instability or induction motor instability by the method when load voltage is greatly reduced after a fault appears. Particular for the voltage instability, because the change characteristic of the load is an important factor which influences the voltage stability after the fault, the method can consider the voltage stability of the system of different load change characteristics. The method can judge the instability essence of the power system under different load change characteristics after the fault appears, can be applied to the stability analysis and the operation control of the power system and is beneficial to system operation and an analyst to analyze the property of the system after the fault, thus the analyst can take an effective safety control measure to improve the stable operation level of the power system.

The invention provides a method for judging whether continuous phase changing of a direct-current system fails on basis of short-circuit ratio dynamic tracking. The method includes the following steps of calculating the ESCR and the MSCR i of an alternating-current system under the condition that the alternating-current system operates normally, calculating the ESCR and the MSCR i of the alternating-current system under the condition that line faults occur and power is cut off, sequencing the line faults, combining the poorest interlocking fault sets, calculating the ESCR 1 and MSCR 1 of the alternating-current system on the condition of interlocking faults, and judging whether phase changing fails. By means of the method, feature analysis is carried out on transient voltage instability accidents which probably exist in existing and planned alternating-current and direct-current hybrid power grids, fault screening and sequencing can be effectively carried out according to hazard degrees of alternating-current faults to stable operation of the direct-current system, by combination of the current transfer situation after the faults, the interlocking fault sets are reasonably built, and failures of continuous phase changing of the direct-current system and received-end power grid voltage instability risks after the faults can be quickly evaluated.

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.

The invention discloses a transient voltage stabilization judgment method based on real-time generalized Thevenin equivalence, which is applied to an electric power system. The method comprises the following steps: obtaining a Jacobian matrix J and an inverse matrix J-1 of a node power equation at a corresponding moment according to voltage and power statuses of the system and a correction system admittance matrix Y' at each moment in a transient process of the electric power system; and further obtaining a relational expression between node voltage variation and load power variation at an equivalent node, obtaining a relational expression between load current variation and the load power variation at the equivalent node, then obtaining a Thevenin equivalence impedance of the corresponding moment, and finally calculating transient voltage stabilization judgment indexes for off-line analysis and on-line status tracking and early warning of the electric power system. The method disclosed by the invention aims to judge whether transient voltage instability occurs in the system by calculating current Thevenin equivalence parameters according to the status of single time section in the transient process of the electric power system, and the method has the characteristics of intuition and accuracy.

The invention provides a stable, real-time and emergent voltage and power angle control method based on a response message. The method comprises steps as follows: step 1, a power angle quantity and a rotation speed quantity of an electric generator in an electrical power system as well as voltage and current amount of an important load bus of a receiving system are acquired in real time; step 2, power angle stability and voltage stability of the system are monitored in parallel simultaneously, the step 3 is executed when the system loses the power angle stability, the step 4 is executed when the system loses voltage stability, and the step 1 is executed when the system is stable; step 3, a retardation area Sc which should be increased to the system is calculated by utilizing a fit power characteristic curve, a generator-shedding measurement amount is determined, and the step 1 is executed; and step 4, the bus voltage amplitude is used as an evidence for judging the severity of voltage instability, the bus load shedding amount is determined according to the difference of the severity of voltage instability, and the step 1 is executed. The provided real-time and emergency control method adopts a parallel judgment manner, so that a stable, real-time and emergency control scheme of voltage and the power angle of an electrical power system is constructed.

The invention discloses a flexible direct current transmission system power coordinate control method. When a DC voltage control station has a possibility or risk of voltage instability, whether the DC voltage control station can be communicated with an active power control station or a frequency control station or not is determined, and a circumstance that the active power control station changes the power actively or that the frequency control station changes the frequency actively is realized respectively under a condition that the DC voltage control station is communicated with the active power control station or the frequency control station and a condition that the DC voltage control station is not communication with the active power control station or the frequency control station, thereby actively changing the transmitted active power, and maintaining the DC voltage stability. The flexible direct current transmission system power coordinate control method avoids a defect that the system loses stability in voltage or even stops operating because the DC voltage station cannot actively change the power, thereby realizing combination of active prevention and passive defense, avoiding a problem of great power and DC voltage oscillation brought about by passive defense only depending on voltage detection, and realizing accurate control for the power in communication at the same time.

A wind turbine-permanent magnet synchronous generator (WT-PMSG) system includes a variable speed permanent magnet synchronous generator and utilizes a static synchronous compensator (STATCOM) connected on the grid side of the system. A PI / PID controller is designed to apply modulation index control signals to the generator side-converter since the modulation index of the generator side-converter has been determined to have the higher controllability to damp the oscillatory modes of the system when the STATCOM is located at the grid side converter. The controller gains are tuned through a frequency based optimization procedure. This configuration dampens voltage instabilities to provide LVRT compliance.

The present invention provides an analysis method for an electrical power system whereby the plurality of buses are grouped into agents, family lines of agents and families of agents based on the reactive reserves depleted when the buses are loaded. Contingencies are then applied to the electrical power system and the reactive reserves are monitored and an exhaustion factor is determined for one or more family lines in one ore more families. A method for selecting double outage that have no solution for each outage that has no solution when the outage is removed in small steps and an additional step has no solution. The boundary case solution is used to assess where, why, and how the contingency causes voltage instability, voltage collapse, and local blackout. Based on this information, the design of voltage rescheduling, active rescheduling, unit commitment, load shedding is determined that can be used as preventive, corrective, or emergency controls in applications such as system design and planning, operation planning, reactive and voltage management, real time control, and Special Protection System Control. Based on this information, solutions can then be applied to the political power system.

A method of voltage instability load shedding, that includes the steps of measuring current and voltage waveforms of an electrical system at a local bus estimating the Thevenin equivalent admittance based on Kalman Filter techniques, then a voltage stability margin index is calculated using the voltage magnitude. The determined Thevenin admittance and the load at the local system bus and the calculated voltage stability margin index is compared with a predetermined threshold value to determine whether to initiate a load shedding action.

Method for avoiding voltage instability in an electrical grid of an offshore wind park, the offshore wind park electrical grid being connected at a first end of a high voltage alternating current (HVAC) transmission and the main land electrical grid being connected at a second end of the HVAC transmission, each of the wind turbines being connected to the wind park electrical grid, the method comprises determining a main land phase angle at or near the second end of the HVAC transmission; measuring an individual wind turbine phase angle at one or more wind turbines; determining the difference between each of the measured individual wind turbine phase angles and the main land phase angle; and determining whether the difference between one of the measured individual wind turbine phase angle and the main land phase angle exceeds a threshold phase angle difference.

The invention provides a dominant power system instability mode recognition method based on real-time measurement response information. According to the method, a dominant instability mode of a system is judged when a power angle instability phenomenon and a voltage instability phenomenon occur at the same time, and a decision basis is provided for subsequent transient stability emergency control. The method includes the steps of determining a power transmission cross section of the multi-machine interconnected electric power system, obtaining real-time measurement information of the power transmission cross section, calculating dominant system variables which can reflect a system instability mode according to the real-time measurement information, calculating the dominant instability mode identification index according to the dominant system variables, and determining the dominant instability mode of the system according to the dominant instability mode identification index. The method is totally based on the real-time measurement information, dynamic properties of the system are considered fully, and the dominant instability mode of the system when the power angle instability phenomenon and the voltage instability phenomenon occur at the same time can be recognized accurately.

The invention discloses a dynamic reactive planning site-selection analysis method and system considering transient voltage stability. The dynamic reactive planning site-selection analysis method comprises the steps of obtaining related data of a power grid firstly; then performing simulation analysis on the transient voltage stability of the power grid, analyzing the power grid faults to determine a transient voltage instability fault set, and dividing the transient voltage instability fault set into multiple transient voltage stable weak regions; next, calculating the dynamic reactive compensation sensitivity under each fault state, and determining the number and locations of the to-be-compensated points of one of the power grid fault weak region through a panning site-location combinational analysis method; and finally, outputting the position scheme of the dynamic reactive planning site-selection to-be-selected points of all the transient voltage stable weak regions. Compared with the prior art, the dynamic reactive planning site-selection analysis method and system are suitable for dynamic reactive planning site-selection in the alternating current / direct current hybrid power grid, have the advantages of high efficiency, simplicity, tight combination with engineering and the like; and in addition, the redundancy of the dynamic reactive planning site-selection to-be-selected compensation points can be effectively prevented.

A light emitting device including a light emitting component is provided, wherein said light emitting comprising an integrated light emitting diode and a semiconductor field effect transistor. The semiconductor field effect transistor may prevent situations such as overheating and voltage instability by controlling a current passing through the light emitting diode as well as enhancing the ability to withstand electrostatic discharge and reducing cost of the light emitting device in multiple aspects.

The invention provides a circuit for eliminating a power-down residual image of an IGZO display panel. The circuit comprises a power supply module, a voltage comparison module, a voltage compensationstabilization module, a control module and a VCOM discharge module. A common electrode voltage VCOM is quickly pulled down to a GND when an IGZO display panel is powered down without adding an external circuit, so that the pixel electrode voltage is reduced, and the discharge speed of the pixel electrode and the common electrode at both ends of a liquid crystal capacitor is accelerated. The phenomenon of shutdown residual images can be effectively eliminated; and the voltage compensation stabilization module can effectively avoid the display abnormality of the IGZO panel due to voltage instability and control the stability of VCOM charge rapid release in the power-down state.

The invention provides a reactive compensation configuration method based on a static and transient voltage stability constraint. The method comprises the following steps: determining level year data; performing reactive delaminating and districting balance analysis; performing static voltage stability analysis; performing transient voltage stability check; and determining reactive compensation configuration. According to the method, reasonable final reactive compensation configuration is provided through comprehensive optimization of the reactive delaminating and districting balance analysis, static voltage stability analysis and transient voltage stability check. Due to the adoption of the method, the accuracy and effectiveness of reactive compensation configuration can be effectively increased, unnecessary investment is avoided, and waste is reduced; and meanwhile, the voltage instability risk resistance of a power grid is improved greatly, and safe, stable, efficient and economic running level of the power grid is raised.

The invention relates to a dynamic compensation method. The dynamic compensation method comprises the first step of sampling three-phase current, three-phase voltage and load current of a system; thesecond step of judging whether the three-phase current of the system is balanced or not, and judging whether the power factor deviates from a set power factor target value or not, judging whether thethree-phase voltage exceeds a voltage set value or not; step 3, judging whether the three-phase voltage exceeds a voltage set value or not; the third step of calculating the current value required tobe converted by each phase when the three-phase current is unbalanced, calculating the reactive current to be compensated when the calculated power factor of the system deviates from the power factortarget value, and calculating the current used for voltage regulation when the three-phase voltage exceeds the voltage set value; and fourth step of firstly adopting an SVC compensation mode, and thenoutputting compensation current by adopting an SVG compensation mode to compensate the system. The dynamic compensation method is realized through a dynamic compensation generating device. Accordingto the invention, the SVC compensation and the SVG compensation are comprehensively utilized, reactive compensation, and three-phase imbalance compensation and voltage instability compensation are effectively, fast and accurately carried out on a system. The cost is relatively low.

The invention discloses an electric power system risk assessment method based on the deterministic analysis. The tide current shifting and node voltage changing caused after a system is disturbed are comprehensively taken into consideration, and a more thorough power grid vulnerability comprehensive analysis index is put forward. The method comprises the following steps that firstly, a system topological structure is analyzed, the tide current distribution of the system after stable running and disturbing is calculated and comprises active tide current and reactive tide current of branch circuits, node voltages and a phase angle difference of the node voltages; secondly, assessment indexes in an assessment system are calculated and comprise a pre-risk assessment factor and a network comprehensive risk assessment factor; thirdly, risk assessment is carried out on an electric power system according to the set index levels. According to the electric power system risk assessment method, the system risk information is more comprehensively reflected, a unified index risk decision is made for tide current threshold-crossing, voltage instability and cascading failure possibly existing in the system, and operators can make rapid and accurate judgment and take measures to guarantee safe and stable running of the system in time.

A circuit for providing a current to an organic light emitting diode comprising: (a) an amorphous silicon field effect transistor having a gate electrode and a drain electrode through which the current is provided to the organic light emitting diode; and (b) a controller for controlling a bias between the gate electrode and the drain electrode to maintain a threshold voltage shift of less than about 1V. The organic light emitting diode is preferably a component in an active matrix.

An embodiment of the present disclosure provides a pixel compensation circuit and method for driving the same, a display panel and a display device. The pixel compensation circuit comprises a resetting module, a data writing module, a compensation module, a driving module and a light emitting device. The embodiment of the present disclosure may prevent from issues of instability of voltage caused by different threshold voltages by cooperative operations of the respective modules of the pixel compensation circuit. When the light emitting device is controlled by the driving module to display, the difference value between a threshold voltage as well as a voltage difference between the control terminal of the compensation module and the output terminal of the compensation module is irrespective of the threshold voltage, so that the voltage supplied to the light emitting device will not be affected by the threshold voltage. Thus, the embodiment of the present disclosure provides a pixel compensation circuit to solve the technical problem of instability of voltages supplied to the light emitting device caused by different threshold voltage Vth, thereby improving uneven displaying of the display panel and being capable of displaying frames with low grey scale by the display panel.

The invention provides a method for judging power angle instability and voltage instability based on the dynamic Thevenin equivalence. When a power system fails and instable, and the voltage is greatly reduced, the system operation and analysts is difficult to judge whether the instable property of the system belongs to the power angle instability or the voltage instability. Based on the dynamic Thevenin equivalence method, the real-time variation of the Thevenin equivalent potential of a load node to be monitored after the failure occurs can be obtained; and compared with the Thevenin equivalent potential, the instable property of the system can be judged. The method can be applied to the on-line analysis control and the off-line emulation analysis of the power system, facilitate the system operation and the analysts to adopt the effective measure in time and improve the safe and stable operation level of the power system.

The invention discloses a micro-grid flexible grid-connected control method based on integrated control on a common connecting point position. An energy storage system and an SSTS are arranged at the position of a PCC, reactive power is sent to the power distribution grid by utilizing complete micro grid and power distribution grid electric quantity information which can be acquired at the common connecting point position of a micro grid and a power distribution network and stored energy provided at the position when voltage sag of the power distribution network occurs, excessive reactive power is consumed during voltage swell, and voltage instability degree is relieved. By means of a solid changeover switch, the micro-grid connection and disconnection switching speed and accuracy are improved. Accordingly, multi-micro-source micro-grid can be friendly connected to the power distribution network in a minimum connection mode and meanwhile has the capacity of assisting the power distribution network to ride through a voltage sag fault.