Owing to the destructive impacts of harmonic currents, the topic of reducing their impacts on power system has attracted tremendous research interests. In this regard, a shunt active power filter (SAPF) is recognized to be the most reliable instrument. It performs by first detecting the harmonic currents that are present in a harmonic-contaminated power system, and subsequently generates and injects corrective mitigation current back into the power system to cancel out all the detected harmonic currents. This means that other than the ability to generate corrective mitigation current itself, it is actually more important to make sure that the SAPF is able to operate in phase with the operating power system, so that the mitigation current can correctly be injected. Hence, proper synchronization technique needs to be integrated when designing the control algorithms of SAPF. This paper critically discusses and analyzes various types of existing phase synchronization techniques which have been applied to manage operation of SAPF; in terms of features, working principle, implementation and performance. The analysis provided can potentially serve as a guideline and provision of information on selecting the most suitable technique for synchronizing SAPF with the connected power system.
Modern technology unintentionally provides resources that enable the trust of everyday interactions to be undermined. Some authentication schemes address this issue using devices that give a unique output in response to a challenge. These signatures are generated by hard-to-predict physical responses derived from structural characteristics, which lend themselves to two different architectures, known as unique objects (UNOs) and physically unclonable functions (PUFs). The classical design of UNOs and PUFs limits their size and, in some cases, their security. Here we show that quantum confinement lends itself to the provision of unique identities at the nanoscale, by using fluctuations in tunnelling measurements through quantum wells in resonant tunnelling diodes (RTDs). This provides an uncomplicated measurement of identity without conventional resource limitations whilst providing robust security. The confined energy levels are highly sensitive to the specific nanostructure within each RTD, resulting in a distinct tunnelling spectrum for every device, as they contain a unique and unpredictable structure that is presently impossible to clone. This new class of authentication device operates with minimal resources in simple electronic structures above room temperature.
A tri-layer soft reflow fabrication method using solvent vapour that resulted in a sub-micrometer resonant tunneling diode is reported in details. The processing steps are simple, time efficient and are all based on conventional i-line photolithography. The tri-layer soft reflow technique is able to shrink the emitter lateral width from 1µm down to 0.35µm (65% reduction) using a solvent at a very low temperature (<50 ˚C). Studies of device's peak current density (J P ) suggests that excellent scalability is achieved as the emitter area reduces from ~29µm 2 down to ~0.5µm 2 with no significant increase in peak voltage (V P ) due to high series resistance normally associated with submicrometer dimensions. The valley current (I V ) however increases due to side-wall damage introduced by the reactive ion etching (RIE) process. As a result, the peak-tovalley-current ratio (PVCR) decreases from 5.0 (6.3) to 3.8 (4.1) in forward (reverse) direction as the emitter area decreases. We therefore successfully demonstrated the fabrication of a sub-micrometer RTD by using a tri-layer soft reflow technique that has the benefit of excellent scalability, high throughput, repeatable and a reliable low cost process.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.