7 results about "Nyquist curve" patented technology

The invention belongs to the field of stability analysis of a grid-connected system of a grid-building converter, and particularly relates to a grid-building converter grid-connected resonance risk analysis method considering virtual impedance, which comprises the following steps: S1, establishing a three-phase time domain differential equation and simplifying the equation into a single-phase equivalent time domain model; converting into a harmonic state space model of the main circuit; s2, constructing a harmonic state space model of a control system comprising an active power control loop and a reactive power control loop; s3, introducing a virtual impedance control link, and correcting the voltage amplitude reference phasor output by the reactive power control loop; deriving an expression of a modulation signal disturbance phasor; s4, obtaining a complete frequency domain admittance model YGSC of the network construction converter considering the influence of the virtual impedance; an open loop gain TGFM of the grid converter grid-connected system is constructed; and S5, drawing a Nyquist curve based on TGFM, and carrying out resonance risk determination. According to the method, the interaction dynamic characteristics of the network building converter and the power grid under the influence of the virtual impedance can be accurately represented, and the resonance risk of the grid-connected system is evaluated.

The invention relates to an electrochemical impedance spectroscopy-based battery health state estimation method, which comprises the following steps of: acquiring EIS data of different batteries with known SOH, and establishing a corresponding Nyquist curve; based on the medium-low frequency band and low frequency band data of the Nyquist curves of the different batteries, determining medium-low frequency Euclidean distances corresponding to the different batteries; fitting to obtain an SOH estimation equation by combining the SOH of different batteries and the Euclidean distance of low and medium frequencies; carrying out EIS test on the to-be-tested battery to obtain battery impedance data, establishing a Nyquist curve of the to-be-tested battery, and determining a low and medium frequency Euclidean distance of the to-be-tested battery; and substituting the low and medium frequency Euclidean distance of the to-be-measured battery into the SOH estimation equation to obtain an SOH value corresponding to the to-be-measured battery. Compared with the prior art, the current health state of the lithium battery can be obtained simply, efficiently and accurately.

The application discloses a kind of stability determination method of power system and unified power quality conditioner.Therein, the method includes: in power system, after injecting disturbance current corresponding to predetermined disturbance frequency to point of common coupling, obtaining point of common coupling voltage signal, grid-side current signal and load-side current signal;Determine the source impedance of grid-side and the load impedance of load-side;According to source impedance and load impedance, determine the return rate matrix;According to return rate matrix, determine the first eigenvalue and the second eigenvalue;Determine the first Nyquist curve corresponding to the first eigenvalue, and the second Nyquist curve corresponding to the second eigenvalue;According to Nyquist curve, determine the stability result of power system at predetermined disturbance frequency.The application solves the technical problem that there is strong limitation when determining whether power system is stable in related technology, and it is difficult to accurately evaluate the true stability degree.

The invention provides an MIMO (Multiple Input Multiple Output) system Nyquist stability judgment method based on dynamic reconstruction of a transfer function, which comprises the following steps of: 1, converting a 2 * 2 impedance model into a complex vector expression by applying a dynamic reconstruction method to obtain an SISO (Single Input Single Output) impedance transfer function with a complete dynamic state; 2, calculating an intersection point of the Nyquist curve and a real axis, judging whether the intersection point of the Nyquist curve and the real axis is located on the right side of a critical point (-1, 0), if so, determining that the system is stable, and otherwise, determining that the system is unstable; and 3, calculating the amplitude margin of the system under the stable working condition, and analyzing the magnitude of the stability margin of the system. According to the impedance analysis method based on dynamic reconstruction provided by the invention, the impedance matrix of the converter MIMO is accurately equivalent to complex vector representation of SISO through a mathematical transformation relation, and the dynamic characteristics of the system are completely reserved while dimension reduction mapping is realized, so that a more accurate stability analysis result is provided. The method has the advantage of universality and can be popularized to various types of converter models.

The invention relates to the technical field of intelligent power grids, and discloses a fan grid-connected oscillation early warning method and system considering impedance time variation and a medium, and the method comprises the steps: firstly, determining an impedance ratio model of a fan grid-connected system, and carrying out the calculation based on a generalized Nyquist stability criterion to obtain a Nyquist curve of an impedance ratio matrix; and then correcting the early warning margin of the criterion on the basis of the criterion to obtain a modified fan impedance expression and impedance ratio matrix. After the impedance time-varying characteristic is considered, the Nyquist curve presents a curve band with a certain width, and the curve band is used as an oscillation early warning impedance criterion. For impedance change differences caused by time-varying characteristics under different operation conditions, the width of a Nyquist curve band also changes, the potential oscillation risk degree of the system is evaluated by using the width of the curve band, a time-varying characteristic index CTI of an impedance criterion is introduced to quantify the width of the curve band, and the quantified curve band width is used as an oscillation risk evaluation index. And early recognition and early warning of the oscillation trend of the fan grid-connected system are realized.

The invention discloses an active power, reactive power and voltage distribution method, system and device and a medium, and the method comprises the steps: constructing an equivalent circuit model of a power system in a Sagomei region, the power system in the Sagomei region comprising a new energy converter, a network-constructed energy storage converter, a load converter and a modular multi-level converter; based on the equivalent circuit model, a Nyquist stability analysis method is adopted to calculate amplitude margins of the power system in the Sagomei region under different steady-state working points so as to quantify the small disturbance stability of the power system in the Sagomei region, and the amplitude margins are defined as distances from an intersection point of a Nyquist curve and a negative real axis to a critical stable point (-1, 0); and respectively designing and executing an active power distribution strategy, a reactive power distribution strategy and a voltage control strategy according to an analysis result of the amplitude margin. The problems that in the prior art, stability quantification means under multiple working conditions are lacked, and a power and voltage coordination control strategy suitable for the multiple working conditions is not formed are solved.

This invention relates to the field of energy storage system technology, specifically to a battery aging detection method and system based on impedance spectroscopy. The battery aging detection method and system based on impedance spectroscopy is characterized by comprising: an adaptive frequency band focusing excitation module; a synchronous sampling and frequency domain transformation module; a spectral morphology feature encoding module; an intra-cluster dynamic baseline module; a temperature compensation module; a normalized weighted scoring module; an aging grading determination module; an aging trajectory prediction module; and an online evolution module for detection configuration. Compared with existing technologies, by using spectral morphology feature encoding, the Nyquist curve is discretized into a sequence of morphological descriptors, retaining the non-parametric aging information lost in ECM fitting, thus improving the sensitivity of early aging detection; through the adaptive frequency band focusing mechanism, the excitation energy is redistributed to the most sensitive frequency band according to the aging feature sensitivity ranking of each frequency band in the previous round of detection, thereby improving the signal-to-noise ratio.