Superconducting Magnet Energy Storage Unit

Uninterruptible power supplies (UPS) have been used to sustain a continuous power supply to certain critical loads protecting them against unexpected power outages as well as over and under voltage conditions. It requires fast response, compensation and instant availability of electrical power. One of important components that considerably affect these characteristics is energy storage units like a battery bank. However, battery is usually distressed by their short lifecycle, late responses in charging or discharging, and environmental problems. In recent years, superconducting magnet energy storage (SMES) unit has been received a great attraction as an energy storage unit instead of conventional batteries due to the dynamic capabilities and long-term lifecycle of SMES. A lot of UPS systems employing SMES unit have been reported and developed. Most of them are focused on high power usually with three-phase applications. Those applications are unlikely to consider on the circuit complexity and production cost because the most important factor is the stabilization of the system rather than the system configuration and cost. However, a case where it is applied to low power applications, the SMES-based UPS system will be more focused on the design of simple and robust circuit with low system cost. Except the SMES itself, the largest cost reduction is achieved by minimizing the number of switching devices used in a power conversion system. Reducing a number of switching devices and other elements in UPS system can save the system cost, and it has several other merits such as superb compactness and higher reliability as well. In this paper, a single-phase DSP-controlled UPS system employing SMES unit is presented to achieve a simple circuit configuration with higher system stability. The proposed power conversion circuit is based on the integration of half-bridge configurations. It can reduce the number of switching devices by applying a common arm scheme. Operational mode and principles are illustrated with useful discussions, and then the validity of the proposed SMES-based UPS system is verified by experiments using a prototype.