The lack of power supplies due to the depletion of environmentally-polluting fossil fuels is a worldwide issue. Energy supplies with renewable sources such as photovoltaic, wind power, tidal, or energy storage devices are being spotlighted. An Energy Storage System (ESS) is a system that uses a battery to supply energy in case of a shortage or to store surplus energy for high-efficiency and economical operation. When power supplied in renewable energy and grid power rapidly fluctuates, Uninterruptible Power Supplies (UPS) can be used by public institutions or companies. As ESS and UPS usage has increased, this paper suggests an integrated ESS and UPS system with 15-kW capacity that can supply power stably and continuously with a 3-phase grid, renewable energy, and a battery.
A boost converter, which boosts the output voltage of a photovoltaic generation system, performs Maximum Power Point Tracking (MPPT) to supply the optimal power despite solar intensity variations. In addition, an isolated bi-directional converter applies Zero Voltage Switching (ZVS) to reduce the switching loss to increase the energy transfer efficiency. The battery performs as an ESS and a UPS to supply stable power to the load.
UPS mode in the integrated ESS and UPS system operation influences the DC-link Constant Voltage (CV) control due to a partially shaded photovoltaic unit or rapid variations in the output power. The voltage of the 3-phase load can be influenced by DC-link voltage fluctuations. Precise loads are necessary for most advanced equipment, because load voltage fluctuations can cause system malfunctions or destruction. In this paper, an improved DC-link voltage control algorithm is suggested to reduce the effect of photovoltaic generation system output voltage fluctuations. The suggested algorithm is robust to voltage fluctuations or other disturbances, and supplies stable power with no additional system configuration elements or increased DC-link capacity.