Energy Storage Systems (ESS) and Distributed Generation (DG) are topics in a large number of recent research works. Moreover, given the increasing adoption of EVs, high capacity EV batteries can be used as ESS, as most vehicles remain idle for long periods during work or home parking. However, the high EV penetration introduces some issues related to the charging power requirements, thereby increasing the peak demand for microgrids where EV chargers are installed. In addition, photovoltaic distributed generation is becoming another issue to deal with in EV charging microgrids. Therefore, this new scenario requires an Energy Management System (EMS) able to deal with charging demand, as well as with generation intermittency. This paper presents an EMS strategy for Microgrids that contain an EV parking lot (EVM), Photovoltaic (PV) arrays, and dynamic loads connected to the grid considering a Point of Common Coupling (PCC). The EVM-EMS utilizes the projections of future PV generation and future demand to accomplish a dynamic programming technique that optimizes the EVs’ charging (G2V) or discharging (V2G) profiles. This algorithm attends to user preferences while reducing the demand grid dependences and improves the microgrid efficiency.
This paper proposes an asymmetrical pulse-width modulation (PWM) strategy for current-fed dual-active bridge (CFDAB) converters applied to energy storage systems (ESS). The ESS application considers low-voltage and high-capacity batteries, for low-power applications, such as data centers, residential photovoltaic systems (PV), and uninterruptable power supplies (UPS). The proposed modulation permits the use of an isolation transformer with negligible leakage inductance and, therefore, avoids the use of auxiliary circuits such as snubbers, active-clamp, or resonant cells. Hence, the converter implementation is simplified. The modulation also benefits the design of the control system because the converter can be modeled and controlled using simple strategies. A straightforward, large-signal model for the battery charge mode, which is valid over all the operation range of the converter, is obtained. Also, the converter operates with a fixed dc bus voltage on both charge and discharge modes. These characteristics represent a significant advantage when the CFDAB with PWM modulation is compared with phase-shifted or frequency modulations, commonly applied in these converters.
Hitherto, zero-current transition (ZCT) and zero-current zero-voltage transition (ZCZVT) inverters have provided desirable switching conditions for main semiconductors, chiefly for minority carrier ones, by means of a current impulse that unavoidably increases the reactive energy of the auxiliary circuit, penalising their efficiency and device ratings. This often offsets the benefits gained by the above-mentioned soft-switching techniques. This study presents a novel family of ZCZVT inverters that overcome this problem by using a non-resonant auxiliary circuit, which is magnetically coupled to the filter inductor, reducing the inverter component count, and associated circuitry. The principles of operation of the ZCZVT inverter with a magnetically coupled auxiliary circuit is presented and analysed. Experimental results from a 1 kW, 40 kHz, laboratory prototype are used to verify the theoretical analysis and also to compare different technologies applied to the auxiliary switches. The ZCZVT inverter with a magnetically coupled auxiliary circuit and MOSFET-based auxiliary switches presented the highest efficiency, achieving 96% at full load, meanwhile its insulated gate bipolar transistor (IGBT)-based counterpart reached 94.2%.
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