Performance analysis of multi-level high voltage direct current converter

<p class="Abstract">The conventional three-phase alternating current (AC) to direct current (DC) converter can be modified using two isolated-gate bipolar transistor (IGBT) as by-pass switches connected to tapping points on the secondary side of the transformer. This scheme yields a reduction in both harmonic contents and reactive volt-ampere absorption. This modified converter possibly eliminates the need for an on-load tap-changer on the converter transformer. The modified AC/DC converter is fully analyzed and implemented under balanced conditions using MATLAB-Simulink. The expressions of the output DC voltage are derived for different cases. The supply current harmonic contents, the reactive power absorption and the power factor have been compared for three schemes; the conventional bridge, the modified bridge using one by-pass IGBT valve and the modified bridge with two by-pass IGBT valves. </p>

Intensifications reactive power during of asymmetric network outages in dual-stator winding generators

<span lang="EN-US">The paper proposes a protection to dual stator generator, reluctance rotor, from asymmetrical fault. Which prevents the dual stator generator, reluctance rotor, from electrical sage through working process in order to avoid any interruption in the generator-grid connection. The procedure consummated with injecting suitable reactive power during the fault period. The proposed method that makes it possible for wind turbine application via dual stator winding generators (DSWRG) synchronous mod to stay connected to the grid during asymmetrical faults. It has been built according to trusted simulating mode considering all tested parameters according to experiment work. The expirment, consider the DC link side stability and care about the behavior and performance of machine side parameter. As well the machineability is evaluated to ride through asymmetrical fault by observing the secondary side current which has a big role in saving grid side converter. The control takes a response within 200 ms after fault trigger recognition. The generator ability of dynamically remaining connected stable and existing in the network, which is sustained a series voltage disturbance by injecting appropriate amount of reactive power. The main interest required in this paper is the capability of a machine to overcome the asymmetrical fault.</span>

A Quasi-Z-Source-Based Inductive Power Transfer System for Constant Current/Constant Voltage Charging Applications

This article proposes a quasi-Z-source (qZS)-based Inductive Power Transfer (IPT) system for Electric Vehicles (EVs) charging applications. The IPT systems use the magnetic field to transfer power between two coils wirelessly, achieving improved reliability, safety and less environmental impact. Compared to the conventional IPT system, the proposed qZS-IPT system simultaneously achieves DC/DC regulation and DC/AC conversion through a single-stage conversion, thus lowering the cost and complexity of the system. Moreover, the reliability of the system is improved thanks to the qZS network shoot-though immunity and the reduced number of switches. To ensure the battery efficient charging and long service life, the constant current/constant voltage (CC/CV) method is considered. With the proposed innovative modulation scheme, the qZS can easily change between buck and boost modes, respectively, lowering or increasing the secondary side current. A theoretical analysis is presented for system design. Simulation results based on a 25 kW (200 V/135 A) low duty EV charger are presented to verify the effectiveness of the proposed scheme. Experimental tests are performed on a 150 W scale-down prototype to validate the analysis and demonstrate the effectiveness of the proposed qZS-IPT system for CC/CV chargers.

Improving the Quality of the Underwater Robot’s Contactless Battery Charging System

A special feature of the contactless battery charging system of an autonomous underwater robot is the use of a transformer with separating primary and secondary windings. As a result, a non-magnetic gap arises, which leads to the need to increase the primary current and the output current of the autonomous inverter. One of the ways to improve the quality of the system is the use of a resonant circuit at the inverter output in combination with the "soft switching" mode of its power switches. The use of resonance on the transformer secondary side also allows you to equalize the current loads of the primary and secondary windings. In this way, a minimum of losses in the inverter is achieved and the power transformer of the system is optimized. This allows you to reduce the size of the system while maintaining the transmitted power, or increase the transmitted power while maintaining the dimensions. The problem solved by using mathematical modelling with verification of the solution adequacy in a full-scale experiment.

Operational Map and Thermal Performance of a Thermosyphon Cooling System for Compact Servers

This paper advances the state-of-the-art in novel passive two-phase systems for more efficient cooling of datacenters and telecom central offices compared to the traditional air-based cooling solutions (e.g. aisle-based containment systems). The proposed passive two-phase technology uses numerous server-level thermosyphons to dissipate the heat generated by critical components, such as central processing units, accelerators, etc., with the flexibility of selecting the rack-level and room-level cooling elements depending on the deployment scenarios. The main goal of this paper is to experimentally investigate the thermal performance and maximum heat removal capability of a server-level thermosyphon for cooling compact servers. The experimental apparatus, built at Nokia Bell Labs, incorporates a single 7-cm high liquid-cooled thermosyphon that fits within a 2U server (smaller form factors can be achieved by a proper design that would further reduce the thermosyphon’s height). The heat source is represented by a pseudo-chip, composed of six parallel cartridge heaters installed in a copper block that incorporates local temperature measurements and is able of dissipating a total power of ≈ 500 W over a footprint area of 3.5 cm × 3.5 cm (corresponding heat flux of ≈ 41 W/cm2). Steady-state experiments were carried out at various heat loads up to 240 W (corresponding heat flux of ≈ 20 W/cm2), filling ratios and secondary side inlet conditions (coolant temperatures and mass flow rates), using R1234ze(E) and deionized water as the working fluids on the primary and secondary side, respectively. Test results demonstrate high heat transfer performance of the server-level thermosyphon over a wide range of conditions, and operating points are identified and classified into an operational map. Thermosyphon-based cooling systems across multiple length scales can significantly improve operation in terms of lowering energy consumption, allowing for higher hardware density, increased processing speed and reliability.

Design and Implementation of a Single-Stage PFC Active-Clamp Flyback Converter with Dual Transformers

This paper proposes an AC/DC single-stage structure by integrating a boost topology and an active clamp flyback (ACF) circuit with power-factor-correction (PFC) function. The PFC function can be achieved by controlling a boost PFC topology operated in the discontinuous conduction mode. With the coordination of active clamping components, a resonant technique is obtained and zero-voltage-switching (ZVS) can be achieved. The proposed converter is combined with the advantages of: (1) compared with two-stage circuit, a single stage circuit decreases the component of the main circuit and reduces the complexity of the control circuit; (2) a boost topology with PFC function operated in discontinuous conduction mode can be accomplished without adding any current detecting technique or detecting input signal; (3) by using the inductor from the PFC stage, ZVS function can be achieved without any additional inductor; (4) the increment of switching frequency facilitates the optimization of power density; (5) the conducting loss at the secondary side can be reduced by adding the synchronous rectification; (6) in this proposed scheme, the dual transformers with series-parallel connection are utilized, the current at the secondary side can be shared for lowering the conduction loss of the synchronous transistors. Finally, a prototype converter with AC 110 V input and DC 19 V/6.32 A (120 W) output under 300 kHz switching frequency is implemented. The efficiency of the proposed converter reaches 88.20% and 0.984 power factor in full load condition.