936 results about "Low-frequency oscillation" patented technology

The invention discloses a power system low-frequency oscillation mechanism analysis method based on micro-disturbance signal oscillation mode recognition. The method comprises the following steps of: providing a basis for judgment of oscillation mechanism types of power grid low-frequency oscillation accidents by using oscillation components provided by micro-disturbance recognition result in the process of a low-frequency oscillation accident; timely discovering a system running weak link and a potential oscillation source by performing statistic analysis on an entire-grid low-frequency oscillation mode oscillation frequency and damping ratio result which is calculated by micro-disturbance recognition in the given running time period; and establishing a corresponding relation between entire-grid oscillation mode characteristic change and system running condition parameter change to provide a basis for system running adjustment by performing multi-variable association analysis on the entire-grid low-frequency oscillation mode oscillation frequency and damping ratio result which is calculated by micro-disturbance recognition in the given running time period and the system running condition parameter.

The invention discloses an electric system low-frequency oscillation detection method. On the basis of the existing nonlinear and non-stable signal empirical mode decomposition algorithm, the improved empirical mode screening algorithm enables the electric system low-frequency oscillation detection method to adapt to low-frequency oscillation signal processing, decomposed eigen mode components are combined with low-frequency oscillation mode physical expression meaning, and accordingly all low-frequency oscillation mode parameters of low-frequency oscillation sampling signals are recognized. The electric system low-frequency oscillation detection method reduces influence of the endpoint effect through improved mixed endpoint forecast, removes overshoot and undershoot by adopting triple B spline interpolation, simultaneously effectively reduces mode aliasing degree, analyzes and detects aliasing mode parameters through refined complex wavelets, controls algorithm screening depth through the improved energy elementary error screening stopping condition, reduces damping loss of mode components, and accordingly effectively improves low-frequency oscillation mode characteristic parameter detection accuracy.

A hybrid navigation satellite receiver and mobile telephone uses only two crystal oscillators. One that operates a master clock around 27-MHz and that consumes milliwatts of power. The other oscillator consumes only microwatts of power and operates continuously on battery power at about 32-KHz. Only the second, low frequency oscillator is kept running during power “off”. On power “restart”, a real-time-clock counter is consulted to cause an estimate of the GPS system time to be regenerated and supplied to the GPS-DSP to quicken its initialization. The master clock is GPS-calibrated, and the accurate clock is used to drive NCO's for the mobile telephone part and host CPU.

A frequency calibration circuit for use in a spread spectrum receiver. The receiver includes circuitry for receiving a spread spectrum signal from a base station and for recovering a network clock signal therefrom, a low frequency oscillator for producing an oscillator clock signal, and a frequency comparator that takes as inputs the network clock signal and the oscillator clock signal and produces a calibration factor based on the difference between the clock signals. A controller coupled to the low frequency oscillator amd the frequency comparator utilizes the calibration factor together with the low frequency oscillator clock signal to output a accurate and precision timed signal thereby being able to accurately require the timing of the paging channel.

The invention discloses an online evaluation method of electric power system dynamic stability. The online evaluation method comprises the steps of step 1, carrying out high-frequency sampling by utilizing a PMU (Power Management Unit), and extracting an oscillation mode for sampling data by utilizing a matrix pencil identification method; step 2, detecting low-frequency oscillation, and emitting low-frequency oscillation warning if a damping ratio of the detected oscillation mode is lower than a set threshold value; step 3, carrying out small perturbation calculation on a system model in a current running mode through a frequency domain analysis method, and obtaining a characteristic value, a characteristic vector, a corresponding unit and participated factor information; and step 4, screening out information of a low-frequency oscillation mode from a small perturbation calculation result according to the low-frequency oscillation mode which is determined by the matrix pencil identification method, regulating a related electric power generator to output, and obtaining tide stability limit of call lines between related domains through time-domain simulation at the same time. According to the online evaluation method disclosed by the invention, the influence of noise is effectively avoided, the identification accuracy is improved, the calculating speed and the calculating efficiency are increased, and the online dynamic safety evaluation effect of the electric power system is obviously improved.

The invention relates to an on-line monitoring method of low-frequency oscillation of a power system. In the on-line monitoring method, parallel filtration calculation is carried out at an oscillation frequency by creatively utilizing time-frequency atom compound band-pass filter function to obtain oscillation mode number, practical oscillation frequency distribution and real-time amplitude information. On the basis of the redundancy of adjacent real-time amplitude information, various oscillation mode amplitudes and decay time constants can be obtained by utilizing least square optimization estimation; based on the obtained oscillation frequency distribution, amplitude and decay time constant, a low-frequency oscillation signal model can be built, wherein only an initial phase and direct-current component amplitude of each mode are unknown; and optimization estimation is carried out on the model by utilizing a particle swarm optimization algorithm to obtain the initial phase and the direct-current component amplitude. The method has good noise robustness, can be used for accurately distinguishing compound oscillation models, is favorable for the strong non-linear mode analysis ofthe power system and is convenient for on-line monitoring and application.

The invention relates to a WAMS (wide area measurement system) based low-frequency oscillation coordinated damping control method for a power system, and belongs to the technical field of low-frequency oscillation analysis and control of power systems. The method includes adopting a hierarchical clustering technology to perform primary region division according to power angle curves or angular velocity curves obtained after preprocessing, performing low-frequency oscillation mode identification on the system on the basis of a Prony identification algorithm, adopting a PSS (power system stabilizer) to inhibit regional oscillation modes for strong correlation generators with generated low-frequency oscillation modes belonging to regional oscillation modes, introducing wide-area signals of other regions for generators with generated low-frequency oscillation modes belonging to inter-region oscillation modes, designing a controller for a reduced mathematic model of an identification system, and solving parameters of the controller by an LMI (linear matrix inequality). By the low-frequency oscillation controller design method, in a regional and hierarchical control mode, coordinated damping control of the power system is realized.

The physiological or mental functioning of a patient is assessed by subjecting a patient to a protocol expected to activate or suppress the neurhormonal systems that regulate blood flow. A physiological signal indicative of the cardiac cycle, such as the electrocardiograph signal, is then monitored in synchrony with performance of the protocol. The physiological signal is processed to quantify the low frequency oscillation during different conditions during the protocol, and the results are interpreted in terms of cardiovascular changes, such as changes in blood flow to active tissues in the body. The results are then compared to normative data to assess the physiological or mental functioning of the patent.

The present invention discloses parameter regulating method of non-linear electricity system stabilizer based on frequency domain test and pertains to the technical field of stability control of electric power system. The present invention is characterized in that: test the non-frequency-compensation linear property curves and test the phase angle under different frequency points in the low frequency vibrating range of 0.2 to 2.0Hz from the output point of the stabilizer to the voltage of the generator after the working condition of tested machine unit is fixed; then calculate the lead and lag angle a 1 of the linear part of the output signals of the stabilizer under different frequencies, added with phase angle that has corresponding frequency property, and then decide whether surpass the lead and lag range relative with Delta Omega axle prescribed by national standard; if not surpass, the feedback factor k1, k2 and k3 of the linear part can be calculated out; then the damping coefficient C1 and the gain coefficient C2 can be decided with critical amplification times method and load phase step method. The present invention is easy to be comprehended by commissioning operators and is easy to be populated.

The invention provides a method for implementing a parallel power system stabilizer (PSS). The parallel PSS of the invention divides compensation frequency domain of the existing PSS into two sections and compensates the compensation frequency domain by two compensation branches respectively, wherein, in one compensation branch, a gain regulating link is used for improving the amplitude of a high-frequency section, while in the other compensation branch, a lag compensation parameter is used for solving the shortage of compensation in a low-frequency section. As the same as the existing PSS, the parallel PSS of the invention can improve the stability of the small perturbation of the system and inhibit the low-frequency oscillation in an interconnected system. Compared with the existing PSS, the parallel PSS of the invention improves the phase-frequency characteristic of the low-frequency section and the amplitude-frequency characteristic of the high-frequency section, thereby widening the working frequency domain of the parallel PSS of the invention, and inhibiting the reactive power fluctuation while the system is in normal operation.

The invention provides an on-line analysis and an aid decision making method for the low-frequency oscillation of an electric power system. According to information which is measured by a PMU and reflects the dynamic process of a power network, such as electric generator power angle, active power, busbar voltage phase angle, circuit active power, transformer active power, and the like, the invention monitors the low-frequency oscillation event of the power network online, identifies an oscillation mode and a strongly relevant machine set, counts participation factors, recognizes the approximate area of an oscillation center, and offers aid decision making information for restraining the oscillation on time. The invention conquers a problem that the analysis of the low-frequency oscillation is difficult since a power network model and a parameter are not exact, changes a situation that the low-frequency oscillation is lack of monitoring and analyzing method as well as can not be fast reacted in the past, and changes a situation that an exact judgment is hard to be made for the lack of the aid decision making method of the low-frequency oscillation in the past. Based on the safety pre-warning system and the aid decision making system of the low-frequency oscillation, important supports can be offered to power network operators for monitoring and analyzing the low-frequency oscillation feature of the power network and treating the low-frequency oscillation event.

The invention concretely discloses a wide area measurement system which is applied to a phasor measurement unit and based on local frequency spectrum analysis, which comprises a WAMS main station, a PMU substation and a power data network; the PMU substation comprises a GPS time service unit, a synchronized phasor acquisition unit, and a data centralized processing unit; the WAMS main station sends measurement and configuration information, measurement information to be detected and thresholds of a plurality of low-frequency oscillation parameters and receives the parameters measured by low-frequency oscillation which exceed the thresholds and return from each PMU substation for comprehensive analysis in order to obtain overall oscillation mode information; the PMU substation also comprises a frequency spectrum analysis unit and a low-frequency oscillation detection unit. The invention also discloses a phasor measurement unit based on the local frequency spectrum analysis. The adoption of the system and device of the invention can realize real-time and rapid low-frequency oscillation detection and analysis of a large-scale electricity grid.

The present invention relates to valve current control method based on modular multi-level converter, this method includes the control of the low frequency oscillations of the current and that of double frequency harmonic component; For said low frequency oscillations of the current, the control method includes some steps as below: first, calculate the half of the sum of the upper arm current and the lower arm current, it is the valve DC current component, said DC current component is arm circulating current; Secondly, comparing the actual value of the arm circulating current to setting value of that, the error is obtained, after some signal processing, additional output set voltage is obtained. For said the double frequency harmonic component of current, the control method includes some steps as below: firstly, figure out capacitor voltage fluctuation prediction value of the sub module; secondly, the output voltage is divided by the sum of the sub module reference voltage and the capacitor voltage fluctuation prediction value, and get the actual output set number of sub module. This method not only can realize stability of the dynamic performance of the system, but also can suppress the arm double frequency harmonic component, at the same time under the abnormal conditions of the AC system; the valve current has good output characteristics.

The invention discloses a method, device and system for inhibiting the low-frequency oscillation of a power system. The method comprises the following steps: determining a system transfer function of an interconnected power system section of a variable-frequency transformer (VFT); determining parameters of a damping controller in accordance with the system transfer function; and using the VFT to inhibit the low-frequency oscillation of the power system based on the parameters of the damping controller. In the method, device and system for inhibiting the low-frequency oscillation of a power system, the control objective is definite, and the parameters of the damping controller can be adjusted in time by simply tracking the response of an analytic system to the turbulence without learning about the specific structure and parameters of the system or solving complicated power system equations. Thus, the invention achieves a favorable effect on inhibiting the low-frequency oscillation in the system, thereby being beneficial to promoting the security and stability of the power grid.

The invention discloses a low-frequency oscillation disturbance source positioning system and a method of a double-fed fan grid-connected system belonging to the technical field of power system stability analysis. The system comprises a sequentially connected information acquisition module, an oscillation source positioning module and an oscillation source position output module. The method comprises acquiring network structure parameters of a grid-connected system of a double-fed fan with virtual inertia control, The dynamic energy model of doubly-fed wind turbine with virtual inertia controlis constructed by injecting bus voltage, generator node current and load node current into the system. The dynamic energy of the components or branches in the oscillation process is obtained, and thepositive and negative and changing trend of the dynamic energy are judged to trace the disturbance source of the low frequency oscillation. A low-frequency oscillation disturbance source position canbe accurately locate by that invention, the function of the fan related control link in the low-frequency oscillation is taken into consideration, and the possible influence on the fan disturbance source is analyze.

The invention belongs to the field of power systems, and in particular to a method which uses an additional damping controller to modulate active and reactive output of a doubly-fed wind generator to increase low-frequency oscillation damping of a grid connection power system of a large-scale wind farm. According to the invention, the method uses auto-disturbance rejection control technology, introduces the theory of data driving control, engineers an additional damping controller of the wind generator, and makes feature signal of the connecting points of a wind farm as input of the additional damping controller which outputs a signal to be added to active and reactive modulation quantity of a machine side current converter. According to the invention, simulation of the method proves that negative damping low frequency oscillation and forced power oscillation are better controlled, and the method has stronger robustness and engineering practicality. The invention provides a novel method for adjusting parameters of a state observer of a second-order non-linear auto-disturbance controller based on broadband concept.

The invention discloses a method for positioning an oscillation disturbance source in a power system. The method comprises the following steps of: acquiring voltage, current, power physical quantity of a plurality of measuring points in a multi-voltage class power grid and meeting the following conditions: 1, whether each measuring point is subjected to low-frequency synchronous power oscillationis monitored in real time, and an oscillation amplitude, a main oscillation mode frequency, main oscillation mode damping, an initial phase of the main oscillation mode and oscillation initial time information are provided; 2, two frequencies in the main oscillation mode of the measuring points which are subjected to low-frequency oscillation accord with the condition that an absolute value of delta f is less than delta Fset; 3, the oscillation initial time of the measuring points which are subjected to low-frequency oscillation has a sequence relationship, and a clear characteristic that theoscillation starting time of measuring points in a low-voltage class power grid is earlier than the oscillation starting time of measuring points in a high-voltage class power grid; and 4, the average frequency fave of the main oscillation mode of each measuring point which is subjected to low-frequency oscillation accords with the condition that fave is more than fmin and less than fmax; and when the conditions are accorded, determining that the power system is subjected to low-frequency oscillation and a local power grid in an area with the earliest oscillation starting time is the oscillation disturbance source.

The invention relates to an online prevention and control method for low-frequency oscillation of an electric power system on the basis of two types of mechanisms. By the method, according to the idea of online pre-decision and real-time matching, low-frequency oscillation of a negative damping mechanism and low-frequency oscillation of a forced resonance mechanism can be monitored, the low-frequency oscillation of the negative damping mechanism can be monitored online and decision supporting information can be provided by utilizing a time-domain online Prony algorithm, a real-time small interference frequency-domain QR (quadrature right-triangle)algorithm, an IRA(irregular repeat-accumulate) algorithm and a characteristic value sensitivity principle; and further, when damping ratio of a capstan oscillation mode is higher than a damping threshold while oscillation exists, transmission rules of the low-frequency oscillation of the forced resonance mechanism and disturbance sources are recognized by a direct method and a hybrid dynamic simulation method which is implemented on the basis of PSD-FDS whole process stability analysis software. By the online prevention and control method which is high in credibility, real-time data source communication is guaranteed, and the low-frequency oscillation of the two types of mechanisms are monitored on line.

The invention discloses on-line monitoring method and device for the insulating state of a power cable. Two factors are mainly considered for the monitoring of the insulating state of the cable, wherein one factor is a low-frequency current value generated by low-frequency oscillation of a power system; and the other factor is a cable medium loss factor value acquired by calculating the phase angle difference between a low-frequency voltage signal and the current signal, which is generated by the oscillation of the power system and seeking an arctangent value. If any one of the two factors is greater than the corresponding insulated safety threshold, the cable has the insulated ageing hidden trouble. By using the low-frequency signal to monitor, the invention has high detection precision and can remarkably reflect the ageing state of the cable; and in addition, the extra superposition power supply is avoided, so that the invention avoids the damage to the safety of a power grid.

The invention discloses a system and a method for controlling neutral point voltage balance with a low frequency oscillation suppression function. The system comprises a multi-level inverter and a digital processing control module, wherein the digital processing control module comprises a sampling unit, a closed-loop control unit and a digital pulse width modulation (DPWM) unit; the output end of the DPWM unit is connected to each switching tube of the bridge arm of each phase of the multi-level inverter. The method comprises the following steps: in each switching period, the sampling unit acquires a direct-current bus voltage signal of the multi-level inverter, and a three-phase voltage signal and a three-phase current signal both output by the multi-level inverter, respectively; the acquired signals are processed by the closed-loop control unit to obtain three-phase modulating waves; the three-phase modulating waves are processed by the DPWM unit to obtain a pulse width modulation control signal which is used for controlling the working state of the switching tube of each phase of the multi-level inverter by virtue of a drive circuit. The system and the method are capable of suppressing the low frequency oscillation of the neutral point voltage of the direct-current bus of the multi-level inverter and realizing the neutral point voltage balance.

The invention discloses a speed controller parameter optimization method in consideration of primary frequency modulation and ultralow-frequency oscillation suppression. According to the method, a single machine infinite system containing an optimized unit and an equivalent infinite power supply is established, a comprehensive optimized index function is established under the stimulation of frequency step signals of the primary frequency modulation test requirement by regarding the unit openness/power response curve rise time, stabilization time and reverse regulation power as performance indexes of primary frequency modulation and regarding damping torque coefficients of a speed controller and a water turbine system in an ultralow frequency band as ultralow-frequency oscillation damping performance indexes, the primary frequency modulation performance and the damping level can be considered by obtained speed controller parameters, and technical means is provided for optimization of the speed controller parameters and suppression of ultralow-frequency oscillation.

The invention provides a modeling method for a generator excited system which comprises the following steps: (1) obtaining the idle load characteristic of the generator, the idle load and the load characteristics of an exciting dynamo, the time constants of the generator and the exciting dynamo, the phase position and frequency characteristic of the generator excited system and the damping effects of low frequency oscillation by experiments; (2) building a field system model; (3) analyzing the obtained basic data to obtain normalized model parameters, building an original simulation model in a Matlab emulator to carry out step response simulation and carrying out corresponding corrections of the parameters in the model according to simulation calculation and field experiment errors until the errors meet the requirements; (4) transforming the parameters into practically useful model parameters in a power system analyzing program and carrying out further correction of the model parameters in the program according to the specific characteristics of the original model. The model parameters of the field system obtained by the invention have the advantage of enough precision, which can really reflect the performance indexes of the field system.

The invention belongs to the technical field of the low-frequency oscillation on-line detection and analysis in an electric power system and provides a low-frequency oscillation modal analysis method, which is based on wide area phasor metrical information and an empirical mode decomposition method and can carry out the on-line detection and node homology grouping toward the complex low-frequency oscillation of the electric power system. The modal analysis method not only has strong adaptability to the complex waveforms of non-linearity, non-stationarity or those containing non-periodic constituents, but also can carry out phase comparison toward nonsine or cosinoidal inherent modal curves which belong to the oscillation mode of the same electric power system but are slightly different in frequency and realize the homology grouping of the nodes participating in each oscillation mode, thus obtaining the power conversion relation among the nodes and the position of an oscillation center or interface.

A navigation-satellite receiver comprises high-sensitivity radio frequency front-end and navigation processor associated with a client CPU. The client CPU runs an operating system that serially communicates with the navigation processor. The client CPU is also able to obtain navigation data system transmissions from a network server and provides such when the direct satellite signals in the high-sensitivity environment are too weak to be demodulated directly. A low power, low frequency oscillator with a watch-type crystal and counter are used as a real time clock to keep time uncertainty under fifty milliseconds when the receiver is hibernating. If the time uncertainty and position uncertainty are below certain maximums when the receiver is re-awakened, then a minimum number of satellites will be needed and making a preliminary z-count to each can be avoided.

The invention discloses a design method of a stabilizer of a power system in the technical field of stable control of the power system. The method comprises the following steps: selecting a variable corresponding to maximum feedback gain from a full-state feedback gain matrix of the system as a primary variable; and adjusting the feedback gain of the primary variable for realizing the control of damping of the system, and setting a zero point of the system in a matching way for adjusting oscillation mode. By adopting the method, low-frequency oscillation of the system is effectively inhibited, the problem that the overall control effect of the stabilizer is affected due to unreasonable pole configuration of a state variable observer when adopting the full-state feedback control is simultaneously avoided, and the good control effect is realized.

The invention relates to a low-frequency oscillation monitoring technology of a large-scale electrical network on the basis of a wide area measurement system (WAMS). The invention combines the advantages of various real-time analysis algorithms in allusion to the limitation that the low-frequency oscillation monitoring system in prior art only can perform offline analysis, so as to disclose an online low-frequency oscillation monitoring system of an electrical network to realize the online monitoring and analysis of the low-frequency oscillation of the electrical network. The low-frequency oscillation monitoring system of the electrical network of the invention is a software function module based on a traditional WAMS system, and comprises a system management module, a data communication module, a real-time monitoring module, a data analysis module and a database module. The invention realizes the real-time recording, real-time displaying and stable analysis functions of the low-frequency oscillation data in the electrical network, and is mainly used for the monitoring and analysis of the large-scale electrical network.