“Sixty years ago I knew everything; now I know nothing; education is a progressive discovery of our own ignorance. Will Durant”



segunda-feira, 29 de maio de 2017

A Practical Study on Three-Level Hybrid SiC/Si Inverters Fabio Brucchi at Infineon Technologies Italia S.r.l. Klaus Sobe and Davide Chiola at Infineon Technologies Austria AG

In today’s PV, UPS and GPI systems, three-phase output inverters are often based on three-level topologies using Silicon IGBTs. This article demonstrates the potential of a hybrid inverter using CoolSiCTM MOSFETs and TRENCHSTOPTM 5 Silicon IGBTs.
State of the Art Three-Level Inverter Topologies Three-level inverters based on Silicon IGBTs are a common design solution giving an excellent cost/performance ratio. As explained in [1]-[3], the technical advantage over the classical two-level B6 inverter represented in Figure 1 (a) is a reduction of switching losses and filtering effort, at the expenses of higher circuit complexity. Two commonly found three-level designs in the low to mid power range are the Neutral Point Clamping Diode and the Neutral Point Clamping Transistor topology, illustrated in figure 1 (b) and (c), respectively.

Figure 1: Commonly used inverter configurations: (a) two-level (B6, Six-Pack) inverter; (b) three-level neutral point clamping diodes (NPC-1, I-Type) inverter; (c) three-level transistor clamped (NPC-2, T-Type) inverter; for each topology only one out of three phases is shown.
As explained in [2], [4] and [5], both three-level topologies have their advantages and disadvantages. While T-Type inverters have fewer semiconductor devices on the current path and thus low conduction losses, I-Type inverters benefit from lower switching losses as there is no need for a relatively slow higher voltage device. Consequently, T-Type inverters are typically found at switching frequencies up to 20-30kHz, I-Type inverters above.

 SiC Technology Changes the Picture

The unique features of Silicon Carbide (SiC) switches were described in [7] and [8] together with the potential impact on applications. With the emerging SiC semiconductor technology the degrees of freedom for the designer become higher, opening the path to new scenarios: fast 1200V SiC switches can make T-Type inverters attractive for higher frequencies and even the transition back to a two-level solution might be considered in order to achieve higher efficiency and reduce the bill of material [6]. In the following sections, the potential of a hybrid T-Type inverter using 1200V CoolSiC™ MOSFETs and 650V TRENCHSTOPTM 5 IGBTs is demonstrated experimentally. The key benefits of this approach are low conduction and switching losses, relatively low effort for output and EMI filtering and – compared to converters with more than three levels – moderate control effort. Test Setup and Conditions Since this article considers the influence of only the power semiconductors on the system efficiency, all measurements were carried out using a single phase test board and a fixed L-C-L output filter designed by Tecnologie Future S.r.l. and Infineon Technologies Austria A.G. The design goals for this platform were a simple component replacement as well as an easy access for thermal and electrical measurements – not a demonstration of power density or a BOM cost reduction. It should be noted that the absolute efficiency values obtained with a single-phase system do not correspond one-to-one to the values of a three-phase and three-wire system, i.e. a system without exposed neutral. First, the core losses of the filters are different and second the modulation scheme cannot use a third-harmonic injection technique. All devices were operated using an Infineon 1EDI60N12AF driver. This compact, isolated, single channel driver is based on the coreless transformer technology, featuring a high common mode transient immunity – a major requirement when dealing with high speed switches. The output voltage of the drivers is provided using a local HF transformer close to the driver that is fed from one resonant AC link. Using the turn-ratio of the transformer, the gate voltages are set to +15V for turn-on and -5V for turn-off. The single phase inverter was operated at a constant DC link voltage of 720VDC providing a voltage of 230VRMS on the output. Using an electric AC load the output current of the inverter was increased in steps of 1,5ARMS every 5 minutes in order to determine the conversion efficiency for different load situations.

sábado, 27 de maio de 2017

A Study on the Failure Mode of the Battery for Energy Storage System Kim Hee-Jung Department of Mechanical Design Engineering Pusan National University

 Entering the 21st century, new & renewable energy, electric vehicle (EV) and energy storage system (ESS) have emerged due to more regulations on CO2 gases and depletion of fossil fuels after climate changes. With a leap towards the 'IT Era,' uninterruptible power supply (UPS) has developed into an essential equipment, an emergency power system designed to prevent a blackout. A key element of these facilities is a secondary battery which can be divided into lead-acid battery, Ni-MH, Ni-Cd and lithium ion battery (LIB). In particular, there have been numerous studies on lithium batteries with the following advantages: i) low price for unit volume and energy density by weight, ii) very stable lead-acid and high energy density, iii) long life expectancy. The valve-regulated lead-acid battery (VRLA) designed for power storage has a long life expectancy that is 3,000 times or more at 70% depth of discharge. Since it is a closed type, it can suppress the decrease of the electrolyte level, making maintenance unnecessary. In this kind of the VRLA designed for power storage (e.g. photovoltaic power generation, wind power generation, load leveling, etc.), battery performance and life are dependent upon lead alloy-based grid casting and electrolyte 'gel' mixing technologies. Regarding energy accumulation for optimum system operation, the technology developed to figure out the progress of battery failure is a key factor. The conventional large stationary lead-acid battery is mostly used as a backup against a blackout. Even though its life expectancy increased to 15 years, it is not appropriate for power storage in which charge and discharge are repeated every day. These lead storage batteries have critical effects on battery life and performances depending on their charging system. Therefore, the design of an optimum charge system is crucial for operating an optimum system. In general, the suitability of an optimum charge system is assessed by measuring the degree of battery aging. Hence, this study attempted to derive the optimum charge system setting after assessing the degree of battery aging under diverse load conditions. According to high-temperature accelerated life testing, battery internal resistance almost doubled compared to the early-stage battery when the rated capacity decreased to 80% or less. At the same time, battery surface temperature increased by almost twice as well. The VRLA/GEL was primarily heated in the middle area. It appeared that a gel electrolyte was dried out because of heating, causing increase in temperature. In LIB, diverse cathode materials have been applied since the lithium ion secondary battery comprised of LiCOO2 was first developed by SONY. However, LiFePO4 and ternary battery are currently used most widely. LiFePO4 is 3.2V in operating voltage and 170mAh/g in theory capacity. Even though it is slightly lower than a ternary battery in terms of energy density, it has a low risk of ignition and explosion. Therefore, it is great in terms of battery safety. With the aforementioned properties, a lithium ion battery is advantageous in industrial battery sectors such as x-EV, ESS and UPS. Even so, LiFePO4 reveals very low electric conductivity as an olivine material (LiMPO4, M=Mn, Ni, Co, Fe). This weakness has been greatly improved by coating the surface of the active material with carbon. However, degradation becomes more severe because of increase in battery internal resistance as a cycle proceeds. The objective of this dissertation was to clarify failure mode of the secondary battery for ESS. Therefore, this study located the source of the heat which occurs at battery charge or discharge, using IR SnapShot Model 525, one of the non-destructive testing (NDT) and analyzed the progress of the degradation. Next, the degradation behavior and durability of lead storage battery were compared through the measurement of battery internal resistance. It was found that battery internal resistance almost doubled compared to the early-stage battery when the rated capacity decreased to 80% or less. At the same time, battery surface temperature increased by almost twice as well. The surface temperature and internal resistance of the lithium battery almost doubled respectively because of problems in the manufacturing process and the materials themselves.

3kW Energy Storage System with Solar Cells for Grid Connection Hong, Seongjun Department of Energy and Power Conversion Engineering UNIVERSITY OF SCIENCE AND TECHNOLOGY 2015

 In the near future, energy storage will play a vital role to enhance the present changing technology. Energy storage with power generation becomes necessary when renewable energy sources are connected to the grid which consequently adjoins to the total energy in the system since utilities require more power when peak demand occurs. This paper describes the operational function of a 3 kW grid-connected residential Energy Storage System (ESS) which is connected with Photovoltaic (PV) at its input side. The system can perform bidirectional functions of charging from the grid and discharging to the grid when power demand becomes high and low respectively. It consists of PV module, Power Conditioning System (PCS) containing a bidirectional DC/DC Converter and bidirectional DC/AC inverter and a Lithium-ion battery pack. ESS Configuration, specifications, and control are described. The bidirectional DC/DC converter tracks the maximum power point (MPPT) and maintains the stability of PV array in case of power deficiency to fulfill the load requirements. The bidirectional DC/AC inverter has good voltage regulation properties like low total harmonic distortion (THD), low electromagnetic interference (EMI), faster response and anti-islanding characteristics. Experimental results satisfy the effectiveness of the proposed system.
Keywords : energy

quinta-feira, 25 de maio de 2017

EnerSolar -SÃO PAULO-Brasil –23 A 25 MAIO 2017

A EnerSolar + Brasil –23 A 25 MAIO 2017- Feira Internacional de Tecnologias para Energia Solar chega em sua 6ª edição apresentando as mais recentes tecnologias, produtos e serviços voltados para o setor de energias sustentáveis, renováveis e limpas. Organizada pela Cipa Fiera Milano, a feira acontece anualmente todo o mês de maio, juntamente com o ECOENERGY – Congresso de Tecnologias Limpas e Renováveis para a Geração de Energia, que em 2017, realizará a sua 7ª edição.