Electrical impedance

About: Electrical impedance is a research topic. Over the lifetime, 36015 publications have been published within this topic receiving 371891 citations. The topic is also known as: electrical impedance & complex impedance.

Frequency Domain Stability Analysis of MMC-Based HVdc for Wind Farm Integration

Abstract: This paper investigates the stability of offshore wind farms integration through a modular multilevel converter-based high-voltage dc (MMC-HVdc) transmission system. Resonances or instability phenomena have been reported in between wind farms and MMC-HVdc systems. They are arguably originated due to interactions between the MMC and the wind power inverters. However, the nature of these interactions is neither well understood nor reported in the literature. In this paper, the impedance-based analytical approach is applied to analyze the stability and to predict the phase margin of the interconnected system. For that, analytical impedance models of a three-phase MMC in a compensated modulation case and a direct modulation case are separately derived using the small-signal frequency domain method. Moreover, the impedance models of the MMC take the circulating current control into account. The derived impedance models are then verified by comparing the frequency responses of the analytical model with the impedance measured in a nonlinear time-domain simulation model developed in MATLAB. The results show that the potential resonances or instability of the interconnected system can be readily predicted through the Nyquist diagrams. In addition, the analysis indicates that the circulating current control of the MMC has a significant impact on the stability of the interconnected system. Finally, the time-domain simulations validate the theoretical analysis.

A high-impedance ground plane applied to a cellphone handset geometry

Abstract: A high-impedance electromagnetic surface is a new type of metallic structure exhibiting high surface impedance and the suppression of propagating surface currents at a particular frequency band. We experimentally characterize such a high-impedance surface designed near 2.4 GHz. We describe an antenna built on such a surface, integrated into a printed circuit board that was designed for the form factor of a portable handset. Measurement shows high radiation efficiency near 2.4 GHz.

An impedance method for dynamic analysis of active material systems

Abstract: This paper describes a new approach to analyzing the dynamic response of active material systems with integrated induced strain actuators, including piezoelectric, electrostrictive, and magnetostrictive actuators. This approach, referred to as the impedance method, has many advantages compared with the conventional static impedance method, has many advantages compared with the conventional static approach and the dynamic finite element approach, such as pin force models and consistent beam and plate models. The impedance approach is presented and described using a simple example, a PZT actuator-driven one degree of freedom spring mass damper system

A Method to Separate Process Contributions in Impedance Spectra by Variation of Test Conditions

Abstract: Many processes contribute to the overall impedance of an electrochemical cell, and these may be difficult to separate in the impedance spectrum. Here, we present an investigation of a solid oxide fuel cell based on differences in impedance spectra due to a change of operating parameters and present the result as the derivative of the impedance with respect to ln(f). The method is used to separate the anode and cathode contributions and to identify various types of processes.