LLCLC Resonant Converter Based Pseudo DC Link Inverter

Technological advancements in solar power systems necessitate highly reliable power inverters with a high efficiency and a small size. An LLC resonant converter-based pseudo Direct Current (DC) link inverters offer these qualities to some extent. The resonant circuits of conventional pseudo DC link inverters lack the ability to attain a zero gain and cannot handle variable frequency control which in turn requires very large filters to produce pure sinusoidal output voltages for grid. The usage of these filters consequences in the enhanced price and size of inverters; moreover, the reliability of inverters is also reduced. We propose a novel topology for a pseudo DC link inverter based on an LLCLC resonant converter. The proposed inverter does not require large filters, because it generates rectified sinusoidal output voltages. An additional parallel LC component is added in series to the resonant circuit, which makes it able to attain a zero gain through an infinite circuit impedance. The 400 W pseudo DC link inverter with a 40 V input and a 400 V output is designed and simulated on OrCAD PSpice software. The results showed that there is a significant improvement in achieving a zero gain. The possible lowest gain achieved is approximately 0.125. The proposed technique attested to be more efficient than those formerly used, subsequently contributing satisfying outcomes.

An improved new transformer type arc suppression reactor

In this paper, to accurately compensate the arc suppression coil, the structure of the transformer is improved. Here, a fixed inductive element is connected in series with the short-circuit winding, which combines with the leakage inductance of the original transformer to form a new short circuit impedance. The improved transformer reduces the manufacturing cost and difficulty of the controllable inductor, reduces the requirements for the winding of the reactor, and makes the manufacturing easier.

Local impedance to guide focal radiofrequency ablation: there is life in the old dog yet

Despite being first described over 30 years ago, focal radiofrequency (RF) continues to be the most widely used energy modality for catheter ablation. The fact that it has managed to hold its own against stiff competition from alternative energy sources used for pulmonary vein isolation (PVI) is down to continuous evolution based on enhancements in our understanding of its biophysical principles. In particular, the advent of contact-force (CF) based integrated indices such as Ablation Index have improved both efficacy and safety. However, a significant limitation of this approach is the absence of tissue feedback during lesion creation, which results in a blunt ‘one-size-fits-all’ approach. This limitation has been further brought into focus by the recent appreciation of the much greater importance of circuit impedance rather than delivered power as a fundamental determinant of RF lesion size.

RESEARCH ON SHORT-CIRCUIT IMPEDANCES OF NEW CONVERTER TRANSFORMER

The short-circuit impedance of converter transformers is one of the most important specifications in HVDC system. Compared with the traditional converter transformers, the new converter transformer has unique windings connection diagrams. Based on the topological structure of the new converter transformer, this paper proposes a new method to establish the mathematical relationship of short-circuit impedances and filters impedances under considering the valve side and grid side shortcircuit conditions. The analysis on short circuit at valve side and grid side shows that short-circuit impedances values are almost the same in both two conditions, so that the impedance of the new converter transformer is symmetrical. Finally, simulation and experimental results verify the correctness of the theoretical analysis.