Modeling and Control of Flywheel Energy Storage system for Uninterruptible Power Supply



Flywheel Energy Storage has attracted new research attention recently in applications like power quality, regenerative braking and uninterruptible power supply (UPS). As a sustainable energy storage method, Flywheel Energy Storage has become a direct substitute for batteries in UPS applications. Inner design of the flywheel unit is shown to illustrate the economical way to construct the system. A comprehensive model of Flywheel energy storage system (FESS) that bridges the gap caused by power outage for critical loads in commercial and industrial areas is presented. The basic circuit consists of bidirectional power converter and flywheel unit coupled with interior permanent magnet synchronous motor (IPMSM). Maximum torque per ampere (MTPA) and flux weakening are used in the control scheme on IPMSM. Detailed block diagrams of the control scheme are given. The FESS for UPS application is modeled, simulated, and analyzed in MATLAB/SIMULINK environment.



  1. Control systems
  2. DC-AC power conversion
  3. Energy storage
  4. Flywheels
  5. Load flow control
  6. Pulse width modulated power converters
  7. Permanent magnet motors




Fig. 1. Basic circuit diagram of the FESS in UPS.



Flywheel speed in charging mode.

Fig. 2. Flywheel speed in charging mode.

Electromagnetic torque of IPMSM

Fig. 3. Electromagnetic torque of IPMSM.

Power grid voltage sag and outage

Fig. 4. Power grid voltage sag and outage

Power failure detection signal.

Fig. 5. Power failure detection signal.

Flywheel speed in discharging mode.

Fig. 6. Flywheel speed in discharging mode.

 DC bus voltage

Fig. 7. DC bus voltage

3-phase voltage of critical load (phase to ground) without FESS.

Fig. 8. 3-phase voltage of critical load (phase to ground) without FESS.

3-phase voltage of critical load (phase to ground) with FESS

Fig. 9. 3-phase voltage of critical load (phase to ground) with FESS



This paper presents a modeling and control method of FESS in UPS system. A cost effective and reliable flywheel design is brought forward to prove the possible mass utilization of FESS in industrial applications. The control algorithm of FESS is described with detailed block diagram, including the torque control of IPMSM that driving the flywheel, voltage sags and outage detection and DC bus regulation. Simulation results are presented to validate the control strategy. Future tasks will include control strategy on mitigating unbalanced voltage sags, parameter variation of IPMSM and experiment verification of the control methods.



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  • Active Power Corp. (2008), “Quantitative Reliability Assessment of Ball Bearings versus Active Magnetic Bearings for Flywheel Energy Storage Systems,” [Online] Available:
  • Morimoto, M. Sanada, and Y. Takeda, “Wide-speed operation of interior permanent magnet synchronous motors with high-performance current regulator,” Industry Applications, IEEE Transactions on, vol. 30, pp. 920-926, 1994.
  • Barbara H Kenny and Peter E Kascak, “DC Bus Regulation with a Flywheel Energy Storage System,” NASA, John H. Glenn Research Center, Lewis Field Cleveland, Ohio, US, Tech Rep. NASA TM-2002-211897-REV102PSC–61, 2003.

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