High voltage insulation design of coreless, planar PCB transformers for multi-MHz power supplies Ole Christian Spro, Student Member, IEEE, Frank Mauseth, Member, IEEE---Department of Electric Power Engineering, Norwegian University of Science and Technology, Trondheim, Norway, Dimosthenis Peftitsis, Senior Member, IEEE

High voltage insulation design of coreless, planar PCB transformers for multi-MHz power supplies Ole Christian Spro, Student Member, IEEE, Frank Mauseth, Member, IEEE, Dimosthenis Peftitsis, Senior Member, IEEE,

 Abstract—This paper investigates the insulation design for printed, planar, coreless, and high-frequency transformers with high isolation-voltage. By using finite element analysis on 2D axial-symmetry, the transformer circuit parameters and electric field distribution are modelled and estimated. Several transformers are designed for an operating frequency of 6.78 MHz. The high frequency, coreless design allows for using thicker insulation material while ensuring a high transformer efficiency. The inclusion of the coupling capacitance in the design optimisation results in several design solutions with the same figure of merit, but with different footprint and isolation voltages. Moreover, high electric fields are identified around the sharp edges of the PCB windings. Finally, the electrical and isolation performance is verified experimentally. The measured electrical properties are close to the simulated values, validating the chosen model. Breakdown tests demonstrate the feasibility of isolation voltage levels up to several tens of kilovolts. The majority of breakdowns occurs at the outer edge of the PCB winding that was identified as a high-field area. Additionally, a concept for grading the electric field of PCB windings is also proposed. Based on the results, the design aspects are discussed in detail for planar, high-frequency isolation transformers with medium-voltage isolation level.

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A Study on the Explosion and Fire Risk of the Lithium Battery by Sang-BoSim Department of Fire and Disaster Prevention Engineering, The graduate School Hoseo University-Asan,Korea -리튬 배터리의 폭발 및 화재 위험성에 관한 연구-

A Study on the Explosion and Fire Risk of the Lithium Battery Sang-BoSim Department of Fire and Disaster Prevention Engineering, The graduate School Hoseo University-Asan,Korea 

 ABSTRACT

 Due to recent development of IT technology, information level of Korea is said to be the world-best. Thus mobile devices such as cell phones, notebook, and tablet PC that could be used without limitations are trending. Along the trend, high energy high density secondary batteries used as the power source for portable devices are also in the spotlight, and among them Lithium battery demand is rising. Generally a Lithium battery should be certified with KS C 8541 (Lithium secondary battery rule) in order to be on the market. However, battery accidents are growing in number and people are raising questions about the safety of the batteries.

Certified Lithium battery’s safety is guaranteed within normal state, but at abnormal states such as damage to protective circuit, the danger rises due to elimination of minimum protection. Recent studies regarding Lithium batteries only measured ignition status for flammable gas, but did not provide detailed analysis. Also, risk analysis according to battery capacity and comparative analysis between the two representative batteries, Lithium Polymer battery and Lithium Ion battery are rarely carried out. Also, research about general danger of Lithium batteries such as ignition at high temperature environment is incomplete.

This study selected five types of Li-Polymer batteries and three types of Li-Ion batteries of different capacity in order to analyze ignition and fire danger according to usage environment. The results are as following.

1. We designed an ignition circuit using IEC type spark ignition test apparatus based on KS C IEC 60079-11 standard in order to measure the explosion hazard of Lithium battery spark discharge. Through measuring the ignition limit of methane, propane, ethylene, and helium, the result showed that gas with higher danger showed more explosion to less number of battery connection. Also, batteries with not Protection Circuit Module (PCM) exploded more often during connection with battery compared with batteries that had protection circuits.

2. An experiment was conduction using a pyrostat based on UL 1642 and KS C 8541 standard in order to measure Lithium battery’s explosion danger at high temperature environment. As the result, Li-Polymer batter with pack type external material had higher risk of explosion compared to cap type Li-Ion battery. Li-Polymer battery had 160~170℃ explosion between 1970~2700 seconds, and the explosion occurred for the electrolytes seeped out from the cracked battery pack after swelling due to evaporation. On the other hand, Li-Ion battery had 176~197℃ explosion between 3000~3800 seconds caused by vaporized electrolyte increasing the pressure within the battery and protruding to the vulnerable positive (+) end.

3. Short circuit was designed in order to measure the temperature increase according to the short circuit current. For batteries with protection circuit, there was no temperature change caused by short circuit current due to current limitation. However, for batteries with no protection circuit, 30.7~35.6A of maximum short circuit current was produced. For Li-Polymer battery, the current fell until 3.9~12.7A after the maximum short circuit current, but increased again to 5.5~17.8A, showing two-step curve pattern. The maximum temperature was 125℃. For Li-Ion battery, the maximum short circuit current fell steeply to 1.3A and decreased steadily, showing a single step curve pattern. It is because the PTC thermistor embed inside limited the flowing current. The maximum temperature was 95℃.

Thus in order to minimize the danger of Lithium battery explosion, the Lithium battery connection number and discharge characteristics should be considered when used at environment with flammable gas. And swelling and explosive characteristics should be considered when using Li-Polymer and Li-Ion batteries at high temperature environment. Also, to prevent hazards caused by mistakes and abnormal statues, a dual safety device of protection circuits are recommended. 

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Investigation of a Multilevel Inverter for Electric Vehicle Applications BY Oskar Josefsson-THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY-Division of Electric Power Engineering Department of Energy and Environment CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden 2015

 Abstract

 Electrified vehicles on the market today all use the classical two-level inverter as the propulsion inverter. This thesis analyse the potential of using a cascaded H-bridge multilevel inverter as the propulsion inverter. With a multilevel inverter, the battery is divided into several parts and the inverter can now create voltages in smaller voltage levels than the two-level inverter. This, among other benefits, reduces the EMI spectrum in the phase cables to the electric machine. It is also shown that these H-bridges can be placed into the battery casing with a marginal size increase, and some addition of the cooling circuit performance. The benefit is that the separate inverter can be omitted. In this thesis, measurements and parameterisations of the battery cells are performed at the current and frequency levels that are present in a multilevel inverter drive system. The derived model shows a great match to the measurements for different operating points and frequencies. Further, full drive cycle simulations are performed for the two analysed systems. It is shown that the inverter loss is greatly reduced with the multilevel inverter topology, mainly due to the possibility to use MOSFETs instead of IGBTs. However, the battery packs in a multilevel inverter experience a current far from DC when creating the AC-voltages to the electric machine. This leads to an increase of the battery loss but looking at the total inverterbattery losses, the system shows an efficiency improvement over the classical two-level system for all but one drive cycle. In the NEDC drive cycle the losses are reduced by 30 % but in the demanding US06 drive cycle the losses are increased by 11 % due to the high reactive power demand at high speed driving. These figures are valid for a plug-in hybrid with a 50 km electrical range where no filter capacitors are used. In a pure electric vehicle, there is always an energy benefit of using a multilevel converter since a larger battery will have lower losses. By placing capacitors over the inputs of the H-bridges, the battery current is filtered. Two different capacitor chemistries are analysed and experimentally verified and an improvement is shown, even for a small amount of capacitors and especially at cold operating conditions.

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Simulating a buck converter closed loop control with PSPICE- Eng. Armando Cavero Miranda-BRAZIL