36 results about "Nyquist curve" patented technology

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.

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 method for suppressing sub-supersynchronous oscillation of doubly-fed fan grid-connected with additional damping control. Aiming at the sub-supersynchronous oscillation phenomenon caused by doubly-fed fan connected to the grid through series-compensated transmission lines, the converter on the rotor side of doubly-fed fan is controlled A second-order low-cut filter is added to the link to suppress its generation. First establish the mathematical impedance model of the double-fed fan with additional damping control in the dq coordinate system, and the impedance model in the dq coordinate system of the equivalent grid; then draw the Nyquis of the system according to the impedance model in the double-fed fan and the grid dq coordinate system By adjusting the damping coefficient of the second-order damper, the Nyquist curve satisfies the generalized Nyquist stability criterion, so that the system is stable. The invention can effectively suppress the sub-supersynchronous oscillation of the fan by adding a second-order low-resistance filter to the control link of the converter on the rotor side of the double-fed fan.

The invention discloses a PID controller parameter control method for an object in a thermal process, comprising the following steps: S1: establishing a high-order transfer function model of the object; S2: establishing an equation by using the asymptote of the Nyquist curve of the open-loop transfer function, Determine the proportional gain k in the PID controller parameters p , the integration time constant T i The relationship with the higher-order transfer function model parameters of the object; S3: Determine the integration time constant T i The relationship between the order n of the higher-order transfer function model and the time constant T of the higher-order transfer function model; S4: Determine the differential time constant T in the PID controller d with the integration time constant T i The relationship between. The invention is simple, fast and has good setting effect.

The invention discloses an aircraft nonlinear attitude control system stability analysis method, and belongs to the field of aircraft attitude control. According to the method, firstly the power coefficient corresponding to the aircraft flight state is calculated, and a corresponding item is expressed by a dead zone threshold h; and then an aircraft linear part transfer function Nyquist curve and a nonlinear part negative converse descriptive function curve are drawn, if the two curves have no intersection point, the nonlinear system is judged to be stable, the value of the pitch channel dead zone threshold h is designed, or the nonlinear system is judged to be instable. According to the method, the stability judgment method for the closed-loop system under different threshold conditions is given so that the stability judgment basis for the closed loop corresponding to the dead zone threshold is theoretically put forward.

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.