Negative impedance converter

About: Negative impedance converter is a research topic. Over the lifetime, 5801 publications have been published within this topic receiving 87636 citations.

High efficiency power converter operating free of an audible frequency range

Abstract: A DC-DC converter operates outside of an audible frequency range under light current load conditions with reduced switching frequency by reducing supply current and regulating output voltage. A control for the converter maintains the switching frequency above an audible frequency range and reduces supply current by modulating switch on-time, sinking supply current, or permitting negative supply current values. The output voltage of the converter is regulated by modulating switch on-time, clamping output voltage, or modifying feedback detector thresholds. The power converter operates with improved efficiency under light current load conditions, while avoiding operation in an audible frequency range to prevent the generation of audible noise in converter components.

Flexible Compensation Strategy for Voltage Source Converter Under Unbalanced and Harmonic Condition Based on a Hybrid Virtual Impedance Method

Abstract: This paper presents a flexible compensation strategy for voltage source converter (VSC) connected to an unbalanced and harmonic distorted grid, which can achieve flexible tradeoff between the two common control targets, i.e., compensating the voltage at the point of common coupling (PCC), and compensating the output current of the VSC. To achieve the control target, a hybrid virtual impedance method is proposed, which uses both the feedforward of the PCC voltage and the feedback of the output current to develop the harmonic (including the negative sequence) voltage references. Compared with the conventional virtual impedance methods using only feedforward or only feedback, the proposed hybrid method can control the harmonic output impedance of the VSC in a wider range, without the potential overmodulation or instability problems caused by the conventional methods when the desired virtual impedance varies in a wide range. The effectiveness and superiority of the proposed strategy is theoretically analyzed and experimentally verified.

A Passive-Impedance-Matching Technology to Achieve Automatic Current Sharing for a Multiphase Resonant Converter

Abstract: A passive-impedance-matching (PIM) technology is proposed to achieve automatic current sharing for multiphase resonant converters through matching the input impedance of each phase. The series inductors (or series capacitors) of each phase are connected in parallel to achieve a couple of virtual resistors including positive and negative resistors and variably series inductors (or capacitors). A virtual positive (or negative) resistor increases (or decreases) the input impedance of the respective phase, and the variably series inductors can also compensate the component tolerance such that the impedance of each phase is matched. The current-sharing performance of the common-inductor two-phase LLC resonant converter (as one example) is evaluated under the first-harmonic-approximation assumption. The virtual positive and negative resistors and variably virtual inductors are calculated. The proposed method can share the primary resonant current and the load current for all phases without any additional circuit and control strategy. The PIM technology is extended to other resonant converter topologies, including common-inductor or common-capacitor series-resonant converter, LCC, CLL resonant converter, etc. A 600-W 12-V common-inductor two-phase LLC resonant converter prototype is built to verify the feasibility and demonstrate advantages of PIM technology.

Load-imposed instability and performance degradation in a regulated converter

Abstract: The stability and performance of a regulated converter is analysed based on its closed-loop output impedance. System theory is used to obtain a set of transfer functions that define the internal stability of an interconnected system consisting of source and load converters. The internal stability is described in terms of the ratio of the output impedance of the source converter and the input impedance of the load converter known as the minor-loop gain. Thus, the closed-loop output impedance of a source converter can be used to define safe operating areas that avoid instabilities in the load impedance. It is shown that the margins associated with the minor-loop gain (i.e. the gain and phase margins) do not generally match the margins of the output-voltage loop gain. The relationship is especially weak at frequencies close to and beyond the crossover frequency of the loop gain. This means that the margins given to the minor-loop gain should be gradually increased as the voltage-loop-gain crossover frequency is approached so as to avoid performance degradation (i.e. changes in margins and crossover frequency) in the supply converter. Experimental evidence is provided based on a buck converter under voltage- and peak-current-mode control.

Fault current detection method

Abstract: A method for measuring the impedance of electrical distribution equipment includes: applying a voltage at a first selected frequency to electrical distribution equipment, waiting a delay time for transient effects to settle, measuring current through the electrical distribution equipment, and selecting additional frequencies to repeat the steps of applying, waiting, and measuring. The method can be implemented, for example, by a meter which includes: a control processor connected to receive and execute instructions, and to output a control signal; a frequency generator for generating a frequency signal having a frequency determined by the control signal; a power amplifier connected to receive the control signal and the frequency signal, the power amplifier outputting a voltage signal to the electrical distribution system through a voltage transformer; and an analog-to-digital converter connected to receive analog feedback voltage signals from the voltage transformer, the analog-to-digital converter outputting a digital feedback voltage signal to the processor.