Flywheels have been used since the Bronze Age as a way to store kinetic energy. Today, with new high speed motor technology, VYCON has developed highly efficient flywheel systems which provide consistent, dependable energy for a variety of important applications. VYCON's flywheel-based energy storage systems hold kinetic energy in a spinning mass, and convert this energy to electric power through the use of a high speed electric motor/generator. Advanced flywheel systems from VYCON originated from its parent company Calnetix, the leader in high speed permanent magnet motors and generators, magnetic bearings, power electronics and system integration.
THE ANATOMY OF A FLYWHEEL SYSTEM
Main components of the VYCON flywheel -- a high-speed permanent magnet motor/generator, fully active magnetic bearings, and the rotor assembly construction -- constitute a unique synthesis of proprietary technologies:
- High Speed Permanent Magnet Motor/Generator. VYCON's motor/generator design utilizes specialized rare earth magnets to minimize rotor heating and maximize efficiency and reliability. This type of motor design allows the VYCON systems to cycle quickly without overheating and can therefore be used in difficult applications with high cycling and long life requirements. The motor/generator is rotated at speeds up to 36,750 RPM where the flywheel system will be at a fully charged state. During discharge the rotor speed decreases to a minimum speed, typically 10,000-12,000 RPM. This speed range is called the discharge range and can be adjusted for more energy or higher cycling depending on the application. The rotor assembly of the flywheel operates in a vacuum provided by an external vacuum pump. By removing air from the rotating area of the motor, all windage losses from the system are eliminated, thereby increasing electrical efficiency.
- The flywheel is designed with a steel mass for storage. Steel offers a well understood, well supported material that offers virtually no technology or availability risks. Other materials such as composites offer higher energy densities with the ability to store more energy, however the potential risk of temperature changes and creep can cause unbalanced loads in the rotor assembly over time degrading operation over the life of the product. The overall construction of the rotor assembly is a key form of intellectual property held by VYCON, Inc. which incorporates aerospace grade steel and magnet materials that upon assembly, behave both mechanically and rotordynamically as a single mass. With this design, the rotor assembly is able to maintain balance and structural integrity as it spins through various critical modes up to its maximum spinning speed.
- Cycling. Based on the permanent magnet motor design, VYCON's flywheel can continuously rapid cycle at rates up to once every minute (e.g.,12 seconds discharge, 18 seconds idle, 12 seconds recharge, 18 seconds idle), and even higher for short durations with longer idle periods. Additionally, the motor produces minimal iron losses in the rotor assembly and therefore minimal heating. Other motor technologies such as switch reluctance machines generate significantly more heat during a discharge, and have difficulty transferring heat from the rotor to the housing due to the vacuum in which the rotor is operating in. Taking advantage of this cycling ability, VYCON is able to apply the flywheel to applications including rail stations, shipyard cranes, and wind power correction among many others.
- Magnetic Bearings/Levitation System. Magnetic bearings allow the motor rotor assembly to rotate at very high speeds with no physical contact to stationary components, thereby taking advantage of the high efficiencies obtainable with high speed rotation. Magnetic bearings levitate the rotating assembly through the force of a magnetic field. The VYCON magnetic bearing design is based on a combination of permanent magnets, which provide a bias field in the gap, and controlled electromagnets which provide the adjustment and centering of the rotor assembly. The position of the rotor assembly is controlled by the magnetic bearing controller which feeds rotor position information from position sensors next to the magnetic bearing actuator. The controller in turn adjusts the current into each coil to reposition the rotor within an allowable orbit. By using this patented magnetic bearing technology, the need for maintenance is virtually eliminated as there are no contact points within the flywheel – no bearings to replace or repack with lubricant. This allows VYCON to offer its flywheel with a 20-year life with no bearing maintenance required.
- Flywheel Power Conversion Module Controller. VYCON's proprietary design of motor and system controls provides high efficiency and maximizes reliability over the flywheel operating life. The flywheel system controller monitors the performance of the flywheel itself, providing a unique control package which can adjust flywheel power levels as required, prevent failures through warning systems and provide users with discharge data and all operating parameters. Controlling the flywheel rotor, the magnetic bearing control system provides continuous status of operational data such as rotating speed, internal temperature and rotor positioning. With self-diagnostic tools, the flywheel system can proactively prevent failures. For each application, flywheel rotational speed limits are modified for the cycling demands and other specific conditions.
- System Management. VYCON's control panel is designed to provide the user with a graphical description of the flywheel storage in real time. The screen provides rotor speed, charged capacity, discharge event history, adjustable voltage settings, RS-232/485 interface, alarm status contacts, soft-start pre-charge from the DC bus and push-button shutdown. Available options include DC disconnect, remote monitoring, Modbus and SNMP communications and real-time monitoring software.
Inside look at the VDC Unit for Power Quality Applications
- Flywheel - Heart of the system providing a 20-year life with no maintenance.
- Master Controller - Monitors output demand and controls the various subsystems including charging (monitoring) and discharging (generating) of the flywheel.
- Magnetic Bearing Controller - Controls the position of the flywheel rotor via a 5-axis active magnetic bearing system.
- Bi-Directional Power Converter - Interface between the DC bus and the variable frequency, variable voltage AC generated by the flywheel.
- Vacuum Pump - Evacuates air within the flywheel to reduce windage losses resulting in increased electrical efficiency.
The VYCON flywheel can be packaged to support various applications. The figure above shows a typical configuration for the VDC and VDC-XE product which supports the critical power market (Data Centers, healthcare facilities, mobile power, industrial plants, casinos and others) as a DC source for UPS systems.
The same flywheel can be repackaged for shipyard cranes, traction power in rail as well as for wind power and smart grid energy storage.