Topic

# Quarter-wave impedance transformer

About: Quarter-wave impedance transformer is a research topic. Over the lifetime, 3740 publications have been published within this topic receiving 46317 citations.

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TL;DR: In this paper, a small-signal impedance modeling of grid-connected three-phase converters for wind and solar system stability analysis is presented, where a converter is modeled by a positive-sequence and a negative-sequence impedance directly in the phase domain.

Abstract: This paper presents small-signal impedance modeling of grid-connected three-phase converters for wind and solar system stability analysis. In the proposed approach, a converter is modeled by a positive-sequence and a negative-sequence impedance directly in the phase domain. It is further demonstrated that the two sequence subsystems are decoupled under most conditions and can be studied independently from each other. The proposed models are verified by experimental measurements and their applications are demonstrated in a system testbed.

765 citations

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TL;DR: In this paper, a unified impedance model of grid-connected voltage-source converters for analyzing dynamic influences of the phase-locked loop (PLL) and current control is proposed, which not only predicts the stability impact of the PLL, but also reveals its frequency coupling effect.

Abstract: This paper proposes a unified impedance model of grid-connected voltage-source converters for analyzing dynamic influences of the phase-locked loop (PLL) and current control. The mathematical relations between the impedance models in the different domains are first explicitly revealed by means of complex transfer functions and complex space vectors. A stationary ( αβ -) frame impedance model is then proposed, which not only predicts the stability impact of the PLL, but also reveals its frequency coupling effect. Furthermore, the impedance shaping effects of the PLL on the current control in the rotating ( dq -) frame and the stationary ( αβ -) frame are structurally comapred. The frequency-domain case studies on a three-phase grid-connected converter are next presented, and subsequently validated in time-domain simulations and experimental tests. The close correlations between the measured results and theoretical analysis confirm the effectiveness of the stationary-frame impedance model.

558 citations

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TL;DR: In this article, a new forbidden region for impedance ratio Z/sub o/Z/sub i/ on the S-plane is proposed as the system stability margin requirement, based on which the impedance specifications of individual loads are established.

Abstract: In a DC distributed power system, the interaction between individually designed power modules/subsystems may cause the instability of the whole system. In a small-signal sense, system level stability is determined by the impedance ratio Z/sub o//Z/sub i/. Here, Z/sub o/ is the output impedance of the source module/subsystem, and Z/sub i/ is the input impedance of the load module/subsystem. As a result, an effective way to prevent system instability is defining impedance specifications for modules/subsystems. This paper briefly summarizes existing works and introduces the authors' contribution in defining impedance specifications. A new forbidden region for impedance ratio Z/sub o//Z/sub i/ on the S-plane is proposed as the system stability margin requirement. Based on this proposed forbidden region, the impedance specifications of individual loads are established. Further, a very practical measurement approach is developed to examine whether or not the system stability margin requirement of the forbidden region is satisfied.

538 citations

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20 Jun 1993

TL;DR: In this paper, a forbidden region for the polar plot of the ratio of impedances at the interface between two cascaded power subsystems is determined, and a method of transforming the forbidden region into a load impedance specification for a given source impedance is developed.

Abstract: By applying the loop gain analysis technique, a forbidden region for the polar plot of the ratio of impedances at the interface between two cascaded power subsystems is determined. A method of transforming the forbidden region into a load impedance specification for a given source impedance is developed. The method assures system stability and minimal performance degradation of the distributed power system, while allowing impedance overlap at the interface. >

504 citations

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TL;DR: In this article, the feasibility of an electrically small transformer with two sections and capable of achieving ideal impedance matching at two arbitrary frequencies is demonstrated analytically, and the exact solution to the resulting transcendental transmission-line equations for two sections is obtained with no restrictions.

Abstract: One of the most useful transmission-line constructs is the quarter-wave transformer that is used to impedance match a line at a single frequency f/sub 0/. The feasibility of an electrically small transformer with two sections and capable of achieving ideal impedance matching at two arbitrary frequencies is demonstrated analytically. To achieve this, the exact solution to the resulting transcendental transmission-line equations for two sections is obtained with no restrictions. The parameters of the transformer are presented in explicit closed form, and are exact. The results of this study are useful for a number of practical design problems, including dual-band antennas and RF circuits in general. In particular, feasibility of ideal operation at the important first harmonic frequency 2f/sub 0/ is demonstrated.

420 citations