A Dynamic Uninterruptible Power Supply (DUPS) with Mechanical Flywheel Storage and Battery

This paper presents a dynamic uninterruptible power supply (DUPS) consisting of both battery and flywheel energy storage systems with the aim of overcoming power quality problems such as temporary voltage drop and power outages. To supply a critical load at the moment of fault occurrence and a few seconds later, the flywheel energy storage system(FESS) and for a few minutes after that or in the case of power outage, the battery storage system and after that, a diesel generator are used respectively. The FESS system consists of a bidirectional inverter, a flywheel and an interior permanent magnet synchronous motor (IPMSM). In the IPMSM control scheme, vector control, torque maximization per ampere(MTPA) and field weakening technics are used. The battery energy storage system consists of a bidirectional DC / DC buck-boost converter and a charge-discharge control. The simulation results show that the FESS changes from standstill to charged and standby condition in less than10  seconds and is ready to supply critical load for short-term phenomena. In UPS mode, it also maintains the critical load voltage at the nominal value in less than one cycle. In the event of a long-term power outage, after discharging the flywheel energy for about 2 seconds, the battery energy storage system maintains the DC link voltage at its reference value and provides the necessary time to start the diesel generator.