No abstract

This paper proposes a three-port grid based dc-to-dc power conversion circuit for low range distributed systems. With this converter, the load can be powered from two different dc sources, which can be a combination of two from a solar-cell panel, a fuel-cell set, a battery bank, etc. and grid source,. The power conversion circuit consists of two active power switches by commonly using an inductor and an output filter capacitor and also the gate pulses of ac inverter circuit. By adjusting the duty-ratio of the active power switch and gate pulses, the voltage regulation at the output as well as the power coordination between two input sources can be made. An experimental circuit has been built and tested to verify the analyzed and simulated results. KEYWORDS: DC-DC converter, Continuous Conduction Mode, Discontinuous Conduction Mode, Grid system I.INTRODUCTIONGenerally, electric power generated by renewable energy sources is unstable in nature, thus producing a bad effect on the utility grid. This fact spurs research on energy storage systems to smooth out active-power flow on the utility grid. Simplified existing energy storage system employing a line-frequency (50-or 60-Hz) transformer, a PWM converter, a bidirectional chopper, and an energy storage device such as electric double layer capacitors (EDLCs) or lithium-ion batteries [1]. The transformer is indispensable for some applications that require voltage matching and/or galvanic isolation between the utility grid and the energy storage device. Replacing the line-frequency transformer with a high-frequency isolated dc-dc converter would make the energy storage system more compact and flexible [2]. Various bidirectional isolated dc-dc converters have been proposed as the interface to energy storage devices with focus on automotive or fuel cell applications. Most of the presented dc-dc converters have asymmetrical circuit configurations to couple the two dc links having largely different voltages, several tens volts and several hundred volts.A bidirectional isolated dc-dc converter presented in 1991. It had two symmetrical single-phase voltage-source full-bridge converters. It suffered from a low efficiency because the first-generation IGBTs were used as switching power devices at that time. However, advancement in power device technology over the last decade has enabled the dcdc converter to operate at an efficiency as high as 97% by using the latest trench-gate IGBTs. A similar dc-dc converter has also achieved an efficiency of 97%. In addition, the use of silicon-carbide power devices in the near future will raise it to 99% [3]. Therefore, the dc-dc converter has become a promising candidate as a power electronic interface for an energy storage system. A bidirectional converter has been discussed to exchange electric power between a fuel cell, a battery, and a load, based on a three-port extension of the circuit presented [4]. The energy storage system using the bidirectional isolated dc-dc converter appropriately choosing the transformer turn rat...