Due to recent technological advances in materials, power electronics, magnetic bearings and controls, the flywheel energy storage system has become a viable alternative to electrochemical batteries. The advantages of the flywheel system are its higher power density, insensitivity to environmental conditions, lack of hazardous materials and ease of checking the charge. One potential use is in a power distribution system. The flywheel energy storage system may be used as both an uninterruptible power supply as well as a means of dynamic voltage compensation to protect critical loads on radial distribution feeders. To perform dynamic voltage compensation, a comparison was performed which shows that the series injection of power is preferable to the shunt injection of power in utilizing the available kVA of the flywheel system motor/generator. The system was designed and modeled using the Electromagnetic Transients Program to ensure a proper dynamic response of the flywheel energy storage system in either mode of operation. The design incorporates a boost converter on the dc link to enable the load voltage to be maintained as the flywheel spins down. The same boost converter also allows for extended operation in the series compensation mode, by implementing a novel control scheme where sinusoidal pulse width modulation control is used for to compensate for smaller supply voltage dips, while the boost converter is used to control the compensation for larger supply voltage dips.
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