Frequency response

About: Frequency response is a research topic. Over the lifetime, 25705 publications have been published within this topic receiving 332249 citations.

Electrosurgical safety circuit and method of using same

Abstract: An improved electrosurgical safety circuit where the currents in the active and patient leads are monitored, the monitored currents being respectively rectified and then subtracted from one another. Whenever the active current exceeds the patient or return current by an amount corresponding to a dynamically variable threshold, an appropriate measure is taken such as the sounding of an alarm and/or the de-energization of the electrosurgical generator. The dynamic threshold varies in accordance with the level of the signal applied to the patient and compensates for leakage current through stray capacitance from the active lead to ground. The patient lead is substantially grounded at radio frequencies through a frequency sensitive network. The frequency sensitive network may include a capacitor, the value of which is such as to provide the foregoing frequency response. Since as small a capacitor as possible must be used to provide a high impedance at low frequencies, and since the radio frequency voltage across the capacitor must be kept low to thereby keep the voltage patient low at radio frequencies, a further network is employed to enable the use of a small capacitor while at the same time decreasing the effective voltage thereacross whereby protection of the patient is enhanced.

Closed-form design and efficient implementation of variable digital filters with simultaneously tunable magnitude and fractional delay

Abstract: This paper proposes a closed-form solution for designing variable one-dimensional (1-D) finite-impulse-response (FIR) digital filters with simultaneously tunable magnitude and tunable fractional phase-delay responses. First, each coefficient of a variable FIR filter is expressed as a two-dimensional (2-D) polynomial of a pair of parameters called spectral parameters; one is for independently tuning the cutoff frequency of the magnitude response, and the other is for independently tuning fractional phase-delay. Then, the closed-form error function between the desired and actual variable frequency responses is derived without discretizing any design parameters such as the frequency and the two spectral parameters. Finally, the optimal solution for the 2-D polynomial coefficients can be easily determined through minimizing the closed-form error function. We also show that the resulting variable FIR filter can be efficiently implemented by generalizing Farrow structure to our two-parameter case. The generalized Farrow structure requires only a small number of multiplications and additions for obtaining any new frequency characteristic, which is particularly suitable for high-speed tuning.

Simultaneous Scheduling of Multiple Frequency Services in Stochastic Unit Commitment

Abstract: The reduced level of system inertia in low-carbon power grids increases the need for alternative frequency services. However, simultaneously optimizing the provision of these services in the scheduling process, subject to significant uncertainty, is a complex task given the challenge of linking the steady-state optimization with frequency dynamics. This paper proposes a novel frequency-constrained stochastic unit commitment model which, for the first time, co-optimizes energy production along with the provision of synchronized and synthetic inertia, enhanced frequency response, primary frequency response and a dynamically-reduced largest power infeed. The contribution of load damping is modeled through a linear inner approximation. The effectiveness of the proposed model is demonstrated through several case studies for Great Britain's 2030 power system, which highlight the synergies and conflicts among alternative frequency services, as well as the significant economic savings and carbon reduction achieved by simultaneously optimizing all these services.

Modeling of Type 3 Wind Turbines With df/dt Inertia Control for System Frequency Response Study

Abstract: A model for Type 3 wind turbines (WTs) with typical d f /dt inertia control is developed for studying frequency dynamics in power systems. A simplified small-signal Type 3 WT model with d f /dt control is first constructed based on the mass-spring-damping concept, such that the physical properties and frequency response of a Type 3 WT can be clearly understood, besides the frequency-domain expressions of the available inertia and the corresponding damping coefficient can be directly derived. The manifested inertia is apparently controllable and frequency-dependent, but differs from the constant inertia featured in a conventional synchronous generator (SG). Furthermore, the frequency response model of a generic two-machine system, composed of an SG and an aggregate Type 3 WTs, is established. The model synthetically considers the effects of the WTs’ different controller parameters, operating points, and the SG's governor response on system frequency characteristics. Then, time-domain simulations on the studied two-machine system are performed in MATLAB/Simulink. The simulated results verify that the proposed model is effective for analyzing system frequency dynamics, and that the test system frequency characteristics can be improved based on tuning the mass-spring- damping coefficients of Type 3 WTs.