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Technology Description

Flywheel Energy Storage Module

The energy storage module is a kinetic-energy-based storage device that contains a flywheel rotor assembly and a motor / generator. This assembly is designed to operate at high speeds (>20,000 RPM) to achieve highest energy storage density (Wh/kg). When power is being removed from the grid the motor/generator converts electric power into mechanical energy to spin the flywheel. When power is required to be delivered to the grid the motor/generator converts this mechanical energy back to electric power. This conversion takes place using commercial high power conversion electronics. A control module is included with each flywheel to regulate current and voltage from each flywheel and to assure all components operate within their prescribed limits.

How the System Will Work

The demonstration FESS is composed of an array of flywheels and motor/generator drives. From each flywheel, two bi-directional inverters are connected back to back to convert the high frequency output/input of the flywheel into a regulated 480 V, 60 Hz input/output that in turn interfaces with a common AC bus. A step-up transformer is required between this common bus at 480 V, and the grid interconnection; since the electrical grid interface is an electrical distribution line at much higher voltage level (i.e. 35, 69, 115 kV). The high voltage side of the transformer is a shunt connected to the high-voltage electric grid bus.

Each flywheel module is associated with an electronic conversion module (ECM). It includes a set of inverters and associated controllers as shown in Figure 5. One inverter will convert the variable speed output form the flywheel Motor /Generator to a D/C buss. The second inverter will convert the D/C buss back to a constant 60 HZ at 480 Vac. The seven ECM’s will operate in parallel and either charge or discharge the flywheels at a power level as directed by the master controller.

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