Output impedance

About: Output impedance is a research topic. Over the lifetime, 11185 publications have been published within this topic receiving 134949 citations.

Implementation of Real-Time Impedance-Based Stability Assessment of Grid-Connected Systems Using MIMO-Identification Techniques

Abstract: Grid impedance has a major effect on the operation of inverter-connected systems, such as renewable energy sources. Stability of such system depends on the ratio of the inverter output impedance and the grid impedance at the point of common coupling. Because the grid impedance varies over time with many parameters, online grid-impedance measurement acquired in real time is most preferred method for observing the stability. Recent studies have presented methods based on multiple-input-multiple-output (MIMO) identification techniques, where the stability of grid-connected system is rapidly assessed in the dq domain. In the methods, orthogonal injections are used with Fourier techniques, and the grid impedance d and q components are measured. The Nyquist stability criterion is then applied to assess the stability. This paper extends previous studies, and presents a real-time implementation for the online stability analysis using MIMO-identification methods. The practical implementation is discussed in detail and experimental results based on a grid-connected three-phase inverter are provided to demonstrate the effectiveness of the methods.

Harmonic interaction analysis in grid connected converter using Harmonic State Space (HSS) modeling

Abstract: An increasing number of power electronics based Distributed Generation (DG) systems and loads generate coupled harmonic as well as non-characteristic harmonic with each other. Several methods like impedance based analysis, which is derived from conventional small signal- and average-model, are introduced to analyze these problems. However, it is found that Linear Time Invariant (LTI) base model analysis makes it difficult to analyze these phenomenon because of time varying system operation trajectories, varying output impedance seen by grid connected systems and neglected switching component during the modeling process. This paper investigates grid connected converter by means of Harmonic State Space (HSS) small signal model, which is modeled from Linear Time varying Periodically (LTP) system. Further, a grid connected converter harmonic matrix is investigated to analyze the harmonic behavior interaction and dynamic transfer procedure. Frequency domain as well as time domain simulation results are represented by means of HSS modeling to verify the theoretical analysis. Experimental results are also included to validate the method.

Improved VCSEL analog optical link

Abstract: An improved analog VCSEL optical link includes the following elements listed in their downstream order from the input to the output: an RF preamplifier (A1) for receiving a bandpass RF signal; a first impedance matching network (LASINT) to match the input impedance of a downstream VCSEL laser to the output impedance of the RF preamplifier (A1); the VCSEL laser coupled to one end of a multimode optical fibre of given length for transducing optically the electrical bandpass RF signal; a PIN diode coupled to the other end of the multimode optical fibre for transducing into electrical the optical signal coming from the fibre; a second impedance matching network (C2, L2) to match the output impedance of the PIN diode to the input impedance of a downstream low-noise transimpedance amplifier (T1) and minimise the noise figure of said transimpedance amplifier (T1) in the meanwhile; the transimpedance amplifier (T1) including a low-noise FET in common source configuration; an RF power amplifier (A2); an RF signal envelope detector generating a control signal for a variable phase shifter placed downstream the RF power amplifier (A2) to compensate for the AM/PM distortion introduced by both the optical fibre and the power amplifier itself; and, if necessary, a gain linearisation network of the RF power amplifier (A2) and/or the RF preamplifier (A1). The analog VCSEL optical link is suitable for the following uses: connecting indoor apparatuses with tower antennas either static, i.e. point-to-point radio relay, or directive arrays, i.e. point-to-multipoint systems; building-up a fibre infrastructure for connecting centralised base stations with respective pool of remote antennas serving as many cells of a cellular telephone system such as: PCS, GSM, UMTS, and similar; intra-building connections for distributing, CATV services (fig.4).

Start up circuit for DC powered field instrument

Abstract: A direct current (DC) powered process instrument start up circuit includes an energy storage device, a switching regulator circuit, a variable impedance circuit, and a voltage measurement circuit. The energy storage device is coupled between first and second power supply terminals. The switching regulator circuit is coupled to the energy storage device and has a regulated voltage output. The variable impedance circuit is coupled between the energy storage device and the first power supply terminal and has an impedance control input. The voltage measurement circuit has a measurement input coupled to the energy storage device and a measurement output coupled to the impedance control input.