36 results about "Nyquist curve" patented technology

The invention relates to a data analysis method for an electrical impedance type quick bacteria detection sensor. According to the data analysis method, based on the electrical impedance principle, the sensor designs and manufactures an interdigital electrode for quickly determining bacteria by using the MEMS (Micro-Electromechanical System) technology; impedance and phase signals collected by the interdigital electrode are processed to obtain a Nyquist curve; the number of the bacteria is well represented by the slope of the Nyquist curve; and the slope change of the Nyquist curve in a bacterial growth process is approximately in a linear relation, thereby establishing a relation between the parameter value and the original bacterium quantity in a sample so as to determine the types and quantity of the bacteria. According to the data analysis method, the requirements on a testing electrode and a measurement environment are reduced, the time for determining the bacteria is shortened, and the data analysis method can be used for quickly detecting microbes.

A method and a pressure chamber for measuring the crack characteristics of damaged rock are provided, wherein the method comprises the steps of: (1) the preparation of a rock test sample; (2) the mounting of the rock test sample: applying a rubber sleeve to the prepared test sample on which upper and lower water permeable conductive press plates and upper and lower waterproof gaskets are mounted previously, respectively, and then mounting the test sample in the pressure chamber so that the lower part of the test sample is flatly connected with the base of the pressure chamber while the upper part thereof is connected to a compression bar through a pressing cap; connecting a lead to the outside, and connecting upstream and downstream water pipes with water inlet and outlet pressure sensors, respectively; and finally, tightly connecting the outer cover of the pressure chamber with the base; (3) the application of a confining pressure and a back pressure: applying the confining pressure to 2-3 MPa according to the sealing requirements of the pressure chamber, so that a rubber film is tightly fitted in with the test sample; next, applying the back pressure of 1 MPa; (4) the hierarchical application of axial pressures: applying the axial pressures step by step according to the intensity of the rock test sample, and testing the stress-strain relationship of the rock under the axial pressure each time and the alternating-current impedance spectroscopy of the rock after the application of the axial pressure each time; and (5) the analysis of damage crack characteristics: analyzing the change law of the damage micro-cracks of the rock according to the characteristic parameters of impedance arcs on alternating-current impedance spectroscopy Nyquist curve. The method and the device are simple, clear in train of thought and convenient to operate.

The invention discloses a global admittance analysis based stability determination method of an APF parallel operation system. The method comprises the following steps of (1) building a current loop and a harmonic control loop admittance model; (2) building a full admittance form equivalent circuit according to the admittance model; (3) obtaining a full admittance expression of the parallel operation system according to a voltage expression of a PCC of a power grid; and (4) drawing an Nyquist curve of full admittance, wherein the stability criteria is as follows: the parallel operation system is stable when positive through frequency and negative through frequency of a negative real axis of an s plane are equal, otherwise the parallel operation system is out of stable. The equivalent form of the above criteria is as follows: all real parts Rd of full admittance gains corresponding to all resonant points of the parallel operation system are larger than 0. According to the stability determination method proposed by the invention, the stability condition of the parallel operation system can be effectively obtained by analyzing frequency-domain characteristic of full admittance, the stability determination method can be used for analyzing the APF parallel operation system under a complicated coupling condition, the fundamental factor affecting the stability of the parallel operation system can be obtained, and the stability determination method has high feasibility and practical value.

The invention discloses a wind power plant grid-connection stability analysis method considering dynamic characteristics of a permanent magnet directly-driven wind turbine generator. The wind power plant grid-connection stability analysis method comprises the steps of S1, building a simplified dynamic model of a PMSG (Permanent Magnet Synchronous Generator) type wind power plant grid-connection system, and acquiring equivalent output impedance of the PMSG type wind power plant grid-connection system; S2, acquiring equivalent input impedance at a grid side of the PMSG type wind power plant grid-connection system by using a Thevenin equivalent method; S3, calculating an output and input impedance ratio Tm of the PMSG type wind power plant grid-connection system; and S4, judging the stability of the PMSG grid-connection system by using an output and input impedance ratio stability analysis principle. From the aspect of frequency domain stability, the wind power plant grid-connection stability analysis method considers main relevant factors of dynamic characteristics of a PMSG, puts forwards a concept of the output and input impedance ratio Tm of the wind power grid-connection system, constructs a specific expression formula of the indicator, and ingeniously uses an Nyquist curve of the output and input impedance ratio Tm to judge the grid-connection stability of the system.

A novel stability analysis method for a cascade system of a three-phase voltage source PWM rectifier and LLC resonant converter is provided. Based on the front-stage PWM rectifier output impedance model and a back-stage LLC resonant converter input impedance model of a cascade system and the impedance ratio stability criterion, the stability of the cascade system can be analyzed by combining theBode diagram and the Nyquist plot. The invention only needs to derive the output impedance of the front-stage converter and the input impedance of the back-stage converter, and can be used for judgingthe stability of the cascade system. This method avoids the drawback that the stability of cascade system can only be judged by simulation curve, and improves the accuracy of stability analysis of cascade system. The stability of the system can be intuitively seen from Bode diagram and Nyquist curve, and the influence of each parameter in the system on the system stability margin can be analyzed,so that the stability margin of the system can be improved.

The invention discloses a method for evaluating the corrosivity of polluted soil. The method comprises the steps of preparing a polluted soil sample, manufacturing a test cutting ring, testing an electrochemical impedance spectrum, evaluating an electrochemical impedance test, fitting a polluted soil equivalent circuit diagram, evaluating a fitting result and evaluating the corrosivity of the polluted soil. An intersection of the Nyquist curve and an impedance real part of the polluted soil sample and the radius of a capacitive reactance arc of the curve are compared under the same test condition; the smaller the intersection is, the smaller the radius of the capacitive resistance arc is, the higher the corrositivity of the polluted soil is; the larger the intersection is, the greater the radius of the capacitive resistance arc is, the lower the corrositivity of the polluted soil is. According to the method for evaluating the corrosivity of the polluted soil, a required test device is simple, the measurement precision is high, and the operation is convenient.

The invention discloses a detection method for analyzing the interfacial electrical properties of a carbon-coated foil. The detection method comprises the following steps: S1, preparation of experimental batteries; S2, formation of the experimental batteries; S3, measurement of the electrochemical impedance spectra of the experimental batteries; and S4, fitting of the impedance spectra of the experimental batteries: carrying out fitting on an impedance spectrum-Nyquist curve by using the measuring software Zahner-4.12USB and the fitting circuit LR (QR) (Q(RW)), and analyzing the influence of an coated-carbon aluminum foil on battery performance through analyzed impedance components. The invention has the beneficial effects that the internal charge transfer resistance of a positive electrode material is analyzed through fitting of the impedance spectra, and the interfacial electrical properties of an aluminum foil-positive electrode material are determined according to the internal charge transfer resistance, so rapid screening can be carried out on raw materials for lithium ion batteries.

The invention provides a method and a device for setting a low-excitation limitation parameter. The method comprises steps: a first characteristic curve for an equivalent transfer function of a generator system along with frequency changes in a set frequency range is acquired through a frequency scanning mode; under a low-excitation limitation parameter of the generator system, a second characteristic curve for a set transfer function of the generator system along with frequency changes in the set frequency range is acquired; the first characteristic curve and the second characteristic curve are used for calculating and acquiring a Nyquist curve for the generator system; and by using the Nyquist curve, the low-excitation limitation parameter is set according to a Nyquist stability criterion. The method and the device can be well applied to field low-excitation limitation parameter setting through the frequency scanning mode, and the stability of the generator system is not broken.

The invention relates to a method for evaluating the rock permeability. The method comprises processes of preparation of a rock test sample, saturation of the rock test sample, test of an electrochemical impedance spectroscopy and evaluation of the permeability of the rock test sample. Middle arcs of rock test sample Nyquist curves under the same test condition are compared; the smaller the radius of the arc is, the higher the rock permeability is; and the larger the radius of the arc is, the lower the rock permeability is. A device required by the method for evaluating the rock permeability is simple. The method for evaluating the rock permeability has high measurement accuracy and is convenient to operate.

The invention discloses a PID controller parameter control method of an object in a thermal process. The method comprises the following steps of: S1: establishing a high-order transfer function model of an object; S2: establishing an equation by using an asymptote of an open-loop transfer function Nyquist curve, and determining the relationship between the proportional gain kp and the integral time constant Ti in the PID controller parameters and the high-order transfer function model parameters of the object; S3: determining the relation between the integral time constant Ti and the order n of the high-order transfer function model and the time constant T of the high-order transfer function model; and S4: determining the relation between the derivative time constant Td and the integral time constant Ti in the PID controller. The PID controller parameter control method is simple, convenient, rapid and has good setting effect.

The invention discloses a method for judging the influence of a power factor on the small-interference stability of a converter grid-connected system. The method comprises the following steps: establishing a converter admittance model and a power grid admittance model by linearly processing a dynamic equation of the converter grid-connected system; forming a single-input single-output closed-loopsystem model by combining the converter admittance model and the power grid admittance model to obtain a closed-loop transfer function of the closed-loop system model; and judging by using a Nyquist curve according to the closed-loop transfer function to obtain a result whether the current running power factor of the converter can enable the converter to run stably or not. The influence of the power factor of the converter on the stability of the grid-connected system can be effectively judged, and the instability problem caused by improper setting of the power factor of the converter is avoided.

The invention discloses a method for judging the operation stability of an onshore doubly-fed wind field through a traditional direct-current sending-out system, which relates to the technical field of renewable energy power generation and transmission, and can realize the operation stability evaluation of the onshore doubly-fed wind field through the traditional direct-current sending-out system.An Nyquist curve of the system is drawn on a complex plane according to the impedance Zwl of the given system and the impedance Zg of the alternating-current power grid; the given system is a traditional direct-current sending-out system for the onshore double-fed wind field; the complex plane is divided into a stable operation feasible region and a stable operation forbidden region according tothe given system stability margin; if the full frequency bands of the Nyquist curve of the given system are in the stable operation feasible region, the given system can be judged to operate stably; and if the Nyquist curve of the given system enters the stable operation forbidden region, an oscillation risk is judged to exist in the given system, so that the given system cannot stably operate atan unstable frequency point, and the unstable frequency point is a frequency point corresponding to the Nyquist curve entering the stable operation forbidden region.

The invention discloses a generalized stability criterion and application method for a power electronic system. When a condition that the number of poles of a system open loop transfer function in a right half plane of an S plane is equal to the number of turns of Nyquist curve anticlockwise surrounding points (-1, j0) of the open loop transfer function is satisfied, a closed-loop system is stable. According to the generalized stability criterion for the power electronic system provided by the invention, the generalized stability criterion is applied to a non-minimum phase system, a criterionapplication range is improved, and accuracy is improved.

The invention discloses a system and a method for judging stability of a tribology system. The system comprises a friction abrasion testing machine, an acceleration sensor, signal acquisition equipment, a noise reduction unit and a central processing unit. The method comprises the following steps: acquiring a friction vibration signal generated in the running process of the tribology system, drawing a Nyquist curve according to the noise after the noise reduction, and judging the stability of the to-be-tested tribology system component according to the characteristics of the Nyquist curve. With the adoption of the technical scheme, the invention is provided with the system and method for judging the stability of the tribology system, the stability detection of the tribology system can be achieved in the friction process without dismantling parts of the friction system or damaging the patterns, the condition that the friction abrasion process cannot be continued because of the test can be avoided. Meanwhile, the system and method has a wide application range and can be applied to the experiment condition in which the lubricating oil is difficult to extract.

The invention provides a virtual admittance method for improving the stability of a grid-tied inverter under a weak grid. The virtual admittance method comprises the steps of S1, determining, according to a d-q admittance model of a grid-tied inverter, an interaction relationship between an inverter and a weak grid, the interaction relationship being that when the impedance of the weak grid is not greater than a first grid impedance value Zg0, a grid-tied system can maintain stability and when the impedance of the weak grid changes to a second grid impedance value Zg, the grid-tied system becomes unstable, where Zg=Zg0+Z'g, Z'g being the change value of the impedance of the weak grid and the change being greater than 0; and S2, measuring the change value Z'g of the impedance of the weak grid online, and connecting a virtual admittance Yp in a control loop of the grid-tied inverter and adaptively adjusting the grid impedance change with the virtual admittance Yp, so that a Nyquist curve of the impedance ratio (Zg0+Z'g) (Yout_cl+Yp) of the grid-tied system is enabled to be the same as Zg0 Yout_cl, Yout_cl being the output admittance of the inverter, the stability of the grid-tied system can be maintained and the stability of the grid-tied inverter under the weak grid is improved. Further, the realized order of the virtual admittance in the control loop can be reduced and the practicality is improved.

The invention discloses a stability determination method of an absolute value system based on a double-sine input description function. The method comprises the following steps: firstly, replacing a derivable nonlinear part of an original system with a Lyapunov linearization result of the derivable nonlinear part; drawing an Nyquist curve of the linear part of the new system; calculating a double-sine input description function of the nonlinear part by adopting a numerical method, drawing a reciprocal curve of the double-sine input description function, analyzing whether the closed-loop systemcan generate periodic oscillation or not according to the intersection condition of the two curves, and amplifying model parameters until the oscillation condition is met if the oscillation cannot begenerated, thereby obtaining the stability margin of the system. According to the method, the limitation of a second-order system, a specific system and the like on the existing method is overcome, and a universal method is provided for researching the stability of an absolute value system.

The invention discloses a thermal power generating unit low-frequency oscillation analysis method considering a nonlinear link. According to the thermal power generating unit considering the dead zone switching link, the stability of the system is judged through a description function method and a stability criterion, and the adopted technical scheme is that firstly, a time domain model of the single-machine infinite bus system is established; secondly, local linearization is carried out on the time domain model to obtain a small interference model, and a block diagram of the small interference model is simplified and transformed to derive a transfer function of a linear part of the single-machine infinite bus system; thirdly, deducing a description function of a dead zone switching link based on the definition of a description function method; and finally, drawing a Nyquist curve of a linear part transfer function of the single-machine infinite bus system and a negative inverse characteristic curve of a dead zone switching link, observing relative positions of the two curves, and judging whether the single-machine infinite bus system is stable or not by combining a stability criterion. The stability of the single-machine infinite bus system can be accurately judged.

The invention relates to a wind power plant stability evaluation method and system based on active equipment node impedance. The method comprises the steps of judging whether impedance models of active equipment and passive equipment are stable or not; determining an active sub-network and a passive sub-network according to the network topology connection relation when the impedance models of the active equipment and the passive equipment are stable; and determining an equivalent open-loop transfer function, judging whether a Nyquist curve of the equivalent open-loop transfer function wraps a (-1, 0j) point or not, if the second judgment result shows that the Nyquist curve of the equivalent open-loop transfer function wraps the (-1, 0j) point, determining an oscillation mode according to the equivalent open-loop transfer function, and calculating an oscillation participation factor of the active equipment according to the oscillation mode; and determining the active equipment with the maximum participation degree according to the oscillation participation factor of the active equipment, and reconfiguring the active equipment with the maximum participation degree. The method effectively reduces the analysis difficulty of the complex network, is easy to expand, and has the advantages of simple and efficient analysis process.