A DC-DC Converter Adequate for Alternative Supply System Applications V. M. Pacheco, L. C. Freitas (IEEE Member), J.B. Vieira Jr. (IEEE Member), E. A. A. Coelho and V.J. Farias Universidade Federal de Uberlândia Faculdade de Engenharia Elétrica – Feelt Campus Santa Mônica - Bloco “ 3N ” 38400-902 – Uberlândia - MG – Brazil Phone/Fax: +55 34 3239-4166 Email: valdeir@ufu.br Abstract: The proposed dc-dc system introduced in this work provides output voltage regulation and control of energy flow between a battery bank and the output dc bus. A simple structure, composed by a dc-dc converter and a battery energy storage, is able to compensate power and voltage fluctuations in supply grid and to provide protection against power outages. The proposed system operates in various modes of operation, according to load needs and supply grid limitations, and is suitable for alternative system applications. A general concept is formulated. Operating principle and theoretical analysis are described. Digital simulation and experimental results of a 1.5 kW, operating at 50 kHz are included for different modes of operation, supporting the validity of the concept. I. INTRODUCTION Battery energy storage has been widely applied in various applications. Uninterruptible Power Supplies (UPS) is a typical application. These systems are standard solution when total outage or voltage sag compensation is required. The topology presented in [1] is an integrated dc UPS topology that combines battery charger and dc-dc converter. The battery charger stage is a buck converter and, when outage occurs, the battery supplies the load in a natural way through a diode connected between the battery and an output capacitor. Over the past decades an interest is growing up about the exploration of renewable energies, such as wind and solar energy, for generation of electrical energy. However, the electric power generated is fluctuating, since the wind presents a random characteristic and the available solar energy depends on the weather conditions. An alternative is to store energy in a battery bank. A model of a wind/diesel system with battery storage bank is proposed in [2] to compensate for the power fluctuations due to the stochastic nature of the wind. In study described in [3] a shunt battery bank injects or absorbs the compensating power to eliminate the ac power component contained in Photovoltaic (PV) array output power. Another growing application is the use of battery storage to limits at a maximum the power delivered by the supply grid. A bi-directional converter for battery energy storage connected with a utility grid operates at energy storage and peak cut modes is presented in [4]. The load-adaptive variable-speed generating system presented in [5] comprises two energy sources: an engine- driven alternator and a battery bank. When the energy from the alternator is insufficient to meet sudden increments in load demand, energy is pumped from the battery to the dc- link. When there is excess engine capacity, the battery energy is replenished. In order to give an additional contribution in this area, this paper proposes a dc-dc converter and a battery energy storage combinated in a simple structure suitable for applications in renewable energy systems. For wind energy the proposed Voltage Regulator - Battery Energy Storage System (VR-BESS), is connected to a generator-turbine by means of an uncontrolled rectifier. In case of solar energy the VR-BESS is connected directly to a photovoltaic array. The VR-BESS is interfaced with the ac utility source by means of a switch-mode dc-ac converter. The proposed system presents the following features: - Voltage regulation, - Peak power leveling, - Protection against outage, - Compensation for power fluctuations. II. SYSTEM DESCRIPTION Fig. 1 shows the block diagram of a general system adequate for renewable energy systems. Note that there are two power stages: dc-dc voltage regulator and battery energy storage. The voltage regulation is accomplished by means of a dc-dc converter, which lifts the supply grid voltage to a regulated output dc bus voltage. 0-7803-7404-5/02/$17.00 (c) 2002 IEEE 1074